user2001: The Keres Attack (Sicilian Scheveningen) has the following starting position
[FEN ""]
[White "Keres Attack"]
[Black "Sicilian Scheveningen"]
1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 e6 6. g4

What are the key ideas for white in this variation? Where should white place the light and heavy pieces? Should the King always castle queenside? What setup should white aim for?

user1105: I have not played this opening ever, and I am not qualified to answer it, I have not found many creditable sources for my answer, but I did manage to find a few. 
I'm not a fan of copy pasting, so here's what I found

How Fearsome is the Keres Attack? By IM Mark Ginsburg
Sicilian Keres Attack: How to crush the Sicilian defence with the
Keres attack
Kasparov vs Karpov, playing this opening and FM FM Eric Schille analyzing it
The Sicilian Scheveningen: Move by Move (Ebook)
Sicilian Scheveningen by GM Magesh and GM Arun

From Ez-net.com, I quote:

The Scheveningen Variation is a classically motivated defense. Black creates a backward pawn center with his duo at d6 and e6, leaving no weakness on the important central squares d5 and e5. Black intends to simply develop his pieces and then proceed with queenside counterplay. The Scheveningen has been a favorite of Kasparov's, although he often arrives at the position through transposition, playing 5…a6 and 6…e6.
  Other top players use the defense frequently and it is well respected, but it doesn't have the devoted following of the Najdorf or Dragon Variations, perhaps because it is too straightforward and logical. White has several ways to combat the Scheveningen Variation, almost all of them leading to dynamic positions.
The Scheveningen Variation, named for a town in Holland, combines …e6 with …d6, instead of the …Nc6…d6 combination of the Classical. The pawn at e6 can serve as a target for White’s tactical operations. Sacrifices of a knight or bishop on that square are almost routine. The most exciting lines start with 6.Bc4 and are known as the Sozin Variation. Opposite wing castling can lead to very double-edged games.
The Scheveningen features the "small center" for Black, with the pawns at d6 and e6 keeping the enemy pieces at bay. For the most part, Black pawns will remain behind the front lines, mostly on the third rank. White will not have very many weaknesses to work against, and precision is required by both sides. For this reason the top player in the world are frequently seen on both sides of the opening.
The much-feared Keres Attack is the greatest disincentive by white to Black's move order. The Keres Attack is the sharpest response to the Scheveningen, favored by attacking players. However it is by no means clear that White has a guaranteed advantage, but the results overwhelmingly favor White. So even Kasparov, who loved to defend the Scheveningen, often arrived via a Najdorf route to avoid the Keres Attack. 
Scheveningen Variation, Keres Attack (with ...h7-h6)(Favors White)
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.g4 White immediately starts his Kingside attack in motion. The threat to play g4-g5 and kick the f6-Knight into oblivion is one that theorists have long debated. Sould Black allow White to carry out his threat, or play ....h7-h6, creating a weakness? This queston produces two distinct variations. Keres Attack (without ....h7-h6) and Keres Attack (with ....h7-h6) the one we will now look at. Scheveningen players by and large prefer to slow down White's expansion by playing
6...h6 7.g5 hxg5 8.Bxg5 At this point is extreamely difficult to evaluate this position. Black's h8-Rook has been "developed" with having moved, a certain plus for Black. The trade of a Black h-pawn for a White g-pawn means that neither player is going to castle on the Kingside. Probably both Kings will move Queenside. White's menacing g5-Bishop must be carefully observed as the tactics of f2-f4 and e4-e5 will hang over Black's position. A usual continuation would be;
8...Nc6 9.f4 Be7 10.Qd2 a6 11.0-0-0 Qc7 12.h4 Bd7 This leads to another one of those bottomless Sicilian positions that defy conventional understanding. Theorists have a slight preference for White in this position.
Scheveningen Variation, Keres Attack (without ...h7-h6) (Favors White)
Black can allow White to carry out his threat, as follows
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.g4 Nc6 7.g5 Nd7 8.Be3 a6 9.h4 Qc7 10.f4 b5
White has extended his Kingside in order to launch an attack, while Black is busily preparing ...Bc8-b7 and ...Nd7-c5 with a counterattack against the e4-pawn. This position is uncommonly sharp. White has a slight advantage. 
Scheveningen Variation, Fischer Attack (Equal Position)
The Fischer Attack is a straight-forward concept that begins
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.Bc4 White tries to clamp down on the d5-square, with an eye toward attacking the e6-pawn with f2-f4-f5. Black has a variety of defenses based upon ...Nb8-c6=a5 or ...Nb8-s7-c5 in conjunction with ...a7-a6 and ...b7-b5-b4 going for the e4-pawn. A solid choice is:
6...Be7 7.Bb3 0-0 8.Be3 White prepares to castle Queenside.
8...Na6 Black decides to bring his Knight to the c5-square to eliminate the b3-Bishop. One of the tactics that Black has to be aware of is; [8...Nbd7 9.Bxe6!? fxe6 10.Nxe6 Qa5 11.Nxf8 Bxf8 White sacrifices two pieces for a Rook.]
9.Qe2 Nc5 10.f3
This is a common position from the Fischer Attack. White will aim for g2-g4-g5 and a big Kingside pawn storm. Black will play ...a7-a6 and ...b7-b5 for an attack on the Queenside. This position is dynamically ballanced. 
Scheveningen Variation, Maroczy Variation (Equal Position)
In the Maroczy Variation, White takes a more restrained approach to the center. He, she, it aims to complete his kingside development, delaying an attack for awhile.
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.Be2 Be7 7.0-0 Nc6 8.Kh1 White tucks his King away to the h1-square. He is committed to playing f2-f4, and wants to avoid tactics based on the g1-a7 diagonal
8...0-0 9.f4 a6 Black guards the b5-square and prepares the c7-square for his Queen.
10.Be3 Qc7
In their 1995 PCA Championship Match, Viswanathan Anand and Garry Kasparov played this position a number of times. The position is dynamically balanced.
Scheveningen Variation, Tal Variation (Equal Position)
1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6
The Tal variation has a completely different plan by White. Mikhail Tal (1936-1992), World Champion, 1960 to 61, was a master of the attack, and introduced the scheme of a quick Queenside castling;
6.f4 White wants to create immediate central threats with e4-e5. Black has to keep a wary, cautious, careful, eye to guarding against this possibility of danger to this possibility.
6...Nc6 7.Be3 Be7 8.Qf3
This position shows Tal's idea. What he wants to do is quickly castle Queenside and reintroduce the threat of e4-e5 after White's Rook is sitting on the d1-square. In many lines, when the players castle on opposite wing, Whit's Queen is ready to support the charge of the g-pawn. The position is dynamically balanced.
There are other plans. White can continue with simple development or go for broke on the kingside with the dangerous Keres Attack, which begins 2…d6; 3d4 cxd4; 4.Nxd4 Nf6; 5.Nc3 g6; 6.g4. Often Black plays this Sicilian defensively, trying to create impregnable barriers. A Hedgehog Position is often the result.


user2042: OK, this one was tough to crack!
I almost gave up, but I believe I have found enough resources to help you grasp the concept of play.

What are the key ideas for white in this variation? 

I think that you will find the answer you seek in this article. The second part is found here and contains relevant moves only-no additional explanations are added.
Still, it tells you enough to grasp the basics.

Should the King always castle queenside?

Yes, otherwise what is the point of g4-it will only weaken the king right ?

Where should white place the light and heavy pieces?  

According to the first part of the above article, bishop goes to g5, the other one's placement depends from the concrete lines, the way I see it. Rooks go to d1 and g1/h3-the latter depending on the circumstances.

What setup should white aim for?

The second part of the above article has a good theoretical coverage in my opinion, but ultimately the decision is yours since I am not an 1.e4 player and my theory knowledge is too rusty. 
As member Fischer suggested, you can use this link to see some master games with commentary and try to learn something from them. Here is the link with some instructive games, in my opinion, that might help you-note the reference to this game in the comments. 
NOTE: Not all the games are about Keres attack but please observe that this is a blog, not a theoretical book.
Another reason for including these links: Being FIDE master yourself, and those guys being IMs, you should have easier time understanding their moves and you should improve faster from those games.
This article mentions several key games for illustrating themes and ideas in Keres attack. To see them you need to register, but with some cleverness we can bypass this:
We know that the games mentioned were played in year 2007 or before, and know the names of the players and the ECO code of the opening. With these information it was not hard for me to find referenced games:
Sokolov-Nisipeanu ( notice that this blog mentions e5 as serious novelty for Black as well-see the commentary bellow the diagram! )
Searching through the same database I found only one game between Macieja and Kasimdzhanov where they played Keres attack so here is the link.
And here is the last game.
These illustrate key ideas for black and ways the White copes with them-positioning of the rooks and minor pieces. For the original commentary of those  you shall have to get by yourself. 
A good thing would be to compare the moves with the current theory, and to use strong engine to analyze the critical middle-game positions in order to reveal the mistakes players made. This should give you better insight about minor piece/rook positioning.
EDIT:
There are no "typical plans" or "typical piece setup" in the Keres attack-only raw calculation and creativity. 
You must be able to adapt to the every change in the position-which is logical-since these are open/semi-open games and that is the quality they require from a player. 
Only closed/semi-closed systems can give you "typical plans/piece setup" which is logical when you think about it, since the closed nature of the position allows you to maneuver. 
In open games things change rapidly, so to ask "typical plans" is pointless, especially in such a dynamic and sharp line like this. I would focus my attention on tactical sharpness.
The way I see it, you can use g4 to force Black into making a concession on the king side and to grab more space. Then you should use your better piece coordination and space advantage to increase your initiative. Playing through the games I see this idea for White over and over. 
This is the way I would approach this problem. 
END OF EDIT
Unfortunately this is all I can offer at the moment, hopefully it will be enough.
Good luck and best regards!

2001: <p>The Keres Attack (Sicilian Scheveningen) has the following starting position</p>

<pre><code>[FEN ""]
[White "Keres Attack"]
[Black "Sicilian Scheveningen"]
1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 e6 6. g4
</code></pre>

<p>What are the key ideas for white in this variation? Where should white place the light and heavy pieces? Should the King always castle queenside? What setup should white aim for?</p>
 1105: <p>I have not played this opening ever, and I am not qualified to answer it, I have not found many creditable sources for my answer, but I did manage to find a few. </p>

<p>I'm not a fan of copy pasting, so here's what I found</p>

<ul>
<li><a href="http://nezhmet.wordpress.com/2007/11/06/how-fearsome-is-the-keres-attack/" rel="nofollow">How Fearsome is the Keres Attack?</a> By IM Mark Ginsburg</li>
<li><a href="http://www.youtube.com/watch?v=d39ZPryEwEE" rel="nofollow">Sicilian Keres Attack: How to crush the Sicilian defence with the
Keres attack</a></li>
<li><a href="http://www.chess.com/article/view/megatheory-9-sicilian-scheveningen" rel="nofollow">Kasparov vs Karpov, playing this opening and FM FM Eric Schille analyzing it</a></li>
<li><a href="http://www.newinchess.com/Shop/Images/Pdfs/8687.pdf" rel="nofollow">The Sicilian Scheveningen: Move by Move (Ebook)</a></li>
<li><a href="http://www.chess.com/article/view/sicilian-scheveningen-by-gm-magesh-and-gm-arun" rel="nofollow">Sicilian Scheveningen by GM Magesh and GM Arun</a></li>
</ul>

<p>From <a href="http://www.ez-net.com/~mephisto/Understanding%20The%20Sicilian%20Defense.html" rel="nofollow">Ez-net.com</a>, I quote:</p>

<blockquote>
  <p>The Scheveningen Variation is a classically motivated defense. Black creates a backward pawn center with his duo at d6 and e6, leaving no weakness on the important central squares d5 and e5. Black intends to simply develop his pieces and then proceed with queenside counterplay. The Scheveningen has been a favorite of Kasparov's, although he often arrives at the position through transposition, playing 5…a6 and 6…e6.
  Other top players use the defense frequently and it is well respected, but it doesn't have the devoted following of the Najdorf or Dragon Variations, perhaps because it is too straightforward and logical. White has several ways to combat the Scheveningen Variation, almost all of them leading to dynamic positions.</p>
  
  <p>The Scheveningen Variation, named for a town in Holland, combines …e6 with …d6, instead of the …Nc6…d6 combination of the Classical. The pawn at e6 can serve as a target for White’s tactical operations. Sacrifices of a knight or bishop on that square are almost routine. The most exciting lines start with 6.Bc4 and are known as the Sozin Variation. Opposite wing castling can lead to very double-edged games.</p>
  
  <p>The Scheveningen features the "small center" for Black, with the pawns at d6 and e6 keeping the enemy pieces at bay. For the most part, Black pawns will remain behind the front lines, mostly on the third rank. White will not have very many weaknesses to work against, and precision is required by both sides. For this reason the top player in the world are frequently seen on both sides of the opening.</p>
  
  <p>The much-feared Keres Attack is the greatest disincentive by white to Black's move order. The Keres Attack is the sharpest response to the Scheveningen, favored by attacking players. However it is by no means clear that White has a guaranteed advantage, but the results overwhelmingly favor White. So even Kasparov, who loved to defend the Scheveningen, often arrived via a Najdorf route to avoid the Keres Attack. </p>
  
  <p><strong>Scheveningen Variation, Keres Attack (with ...h7-h6)(Favors White)</strong></p>
  
  <p><strong>1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.g4</strong> White immediately starts his Kingside attack in motion. The threat to play g4-g5 and kick the f6-Knight into oblivion is one that theorists have long debated. Sould Black allow White to carry out his threat, or play ....h7-h6, creating a weakness? This queston produces two distinct variations. Keres Attack (without ....h7-h6) and Keres Attack (with ....h7-h6) the one we will now look at. Scheveningen players by and large prefer to slow down White's expansion by playing</p>
  
  <p><strong>6...h6 7.g5 hxg5 8.Bxg5</strong> At this point is extreamely difficult to evaluate this position. Black's h8-Rook has been "developed" with having moved, a certain plus for Black. The trade of a Black h-pawn for a White g-pawn means that neither player is going to castle on the Kingside. Probably both Kings will move Queenside. White's menacing g5-Bishop must be carefully observed as the tactics of f2-f4 and e4-e5 will hang over Black's position. A usual continuation would be;</p>
  
  <p><strong>8...Nc6 9.f4 Be7 10.Qd2 a6 11.0-0-0 Qc7 12.h4 Bd7</strong> This leads to another one of those bottomless Sicilian positions that defy conventional understanding. Theorists have a slight preference for White in this position.</p>
  
  <p><strong>Scheveningen Variation, Keres Attack (without ...h7-h6) (Favors White)</strong></p>
  
  <p>Black can allow White to carry out his threat, as follows</p>
  
  <p><strong>1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.g4 Nc6 7.g5 Nd7 8.Be3 a6 9.h4 Qc7 10.f4 b5</strong></p>
  
  <p>White has extended his Kingside in order to launch an attack, while Black is busily preparing .<strong>..Bc8-b7</strong> and .<strong>..Nd7-c5</strong> with a counterattack against the <strong>e4-pawn</strong>. This position is uncommonly sharp. White has a slight advantage. </p>
  
  <p><strong>Scheveningen Variation, Fischer Attack (Equal Position)</strong></p>
  
  <p>The Fischer Attack is a straight-forward concept that begins</p>
  
  <p>1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.Bc4 White tries to clamp down on the d5-square, with an eye toward attacking the e6-pawn with f2-f4-f5. Black has a variety of defenses based upon ...Nb8-c6=a5 or ...Nb8-s7-c5 in conjunction with ...a7-a6 and ...b7-b5-b4 going for the e4-pawn. A solid choice is:</p>
  
  <p><strong>6...Be7 7.Bb3 0-0 8.Be3</strong> White prepares to castle Queenside.</p>
  
  <p>8...Na6 Black decides to bring his Knight to the c5-square to eliminate the b3-Bishop. One of the tactics that Black has to be aware of is; [8...Nbd7 9.Bxe6!? fxe6 10.Nxe6 Qa5 11.Nxf8 Bxf8 White sacrifices two pieces for a Rook.]</p>
  
  <p><strong>9.Qe2 Nc5 10.f3</strong></p>
  
  <p>This is a common position from the Fischer Attack. White will aim for <strong>g2-g4-g5</strong> and a big Kingside pawn storm. Black will play ...a7-a6 and ...b7-b5 for an attack on the Queenside. This position is dynamically ballanced. </p>
  
  <p><strong>Scheveningen Variation, Maroczy Variation (Equal Position)</strong></p>
  
  <p>In the Maroczy Variation, White takes a more restrained approach to the center. He, she, it aims to complete his kingside development, delaying an attack for awhile.</p>
  
  <p>1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6 6.Be2 Be7 7.0-0 Nc6 8.Kh1 White tucks his King away to the h1-square. He is committed to playing f2-f4, and wants to avoid tactics based on the g1-a7 diagonal</p>
  
  <p>8...0-0 9.f4 a6 Black guards the b5-square and prepares the c7-square for his Queen.</p>
  
  <p>10.Be3 Qc7</p>
  
  <p>In their 1995 PCA Championship Match, Viswanathan Anand and Garry Kasparov played this position a number of times. The position is dynamically balanced.</p>
  
  <p><strong>Scheveningen Variation, Tal Variation (Equal Position)</strong></p>
  
  <p>1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e6</p>
  
  <p>The Tal variation has a completely different plan by White. Mikhail Tal (1936-1992), World Champion, 1960 to 61, was a master of the attack, and introduced the scheme of a quick Queenside castling;</p>
  
  <p>6.f4 White wants to create immediate central threats with e4-e5. Black has to keep a wary, cautious, careful, eye to guarding against this possibility of danger to this possibility.</p>
  
  <p>6...Nc6 7.Be3 Be7 8.Qf3</p>
  
  <p>This position shows Tal's idea. What he wants to do is quickly castle Queenside and reintroduce the threat of e4-e5 after White's Rook is sitting on the d1-square. In many lines, when the players castle on opposite wing, Whit's Queen is ready to support the charge of the g-pawn. The position is dynamically balanced.</p>
  
  <p>There are other plans. White can continue with simple development or go for broke on the kingside with the dangerous Keres Attack, which begins 2…d6; 3d4 cxd4; 4.Nxd4 Nf6; 5.Nc3 g6; 6.g4. Often Black plays this Sicilian defensively, trying to create impregnable barriers. A Hedgehog Position is often the result.</p>
</blockquote>
 2042: <p>OK, this one was tough to crack!</p>

<p>I almost gave up, but I believe I have found enough resources to help you grasp the concept of play.</p>

<blockquote>
  <p>What are the key ideas for white in this variation? </p>
</blockquote>

<p>I think that you will find the answer you seek in <a href="http://chesscoach1950.blogspot.com/2006/06/chess-understanding-sicilian.html" rel="nofollow">this</a> article. The second part is found <a href="http://chesscoach1950.blogspot.com/2007/02/chess-understanding-sicilian.html" rel="nofollow">here</a> and contains relevant moves only-no additional explanations are added.</p>

<p>Still, it tells you enough to grasp the basics.</p>

<blockquote>
  <p>Should the King always castle queenside?</p>
</blockquote>

<p>Yes, otherwise what is the point of <code>g4</code>-it will only weaken the king right ?</p>

<blockquote>
  <p>Where should white place the light and heavy pieces?  </p>
</blockquote>

<p>According to the first part of the above article, bishop goes to <code>g5</code>, the other one's placement <strong>depends from the concrete lines</strong>, the way I see it. Rooks go to <code>d1</code> and <code>g1/h3</code>-the latter depending on the circumstances.</p>

<blockquote>
  <p>What setup should white aim for?</p>
</blockquote>

<p>The second part of the above article has a good theoretical coverage in my opinion, but ultimately the decision is yours since I am not an <code>1.e4</code> player and my theory knowledge is <strong>too rusty.</strong> </p>

<p>As member <em>Fischer</em> suggested, you can use <a href="https://nezhmet.wordpress.com/category/chess-openings/sicilian-defense/scheveningen/keres-attack/" rel="nofollow">this</a> link to see some master games with commentary and try to learn something from them. <a href="http://nezhmet.wordpress.com/2007/12/14/the-fabulous-00s-more-defending-vs-the-keres-attack/" rel="nofollow">Here</a> is the link with some instructive games, <strong>in my opinion</strong>, that might help you-note the reference to <a href="http://nezhmet.wordpress.com/2008/03/20/the-fabulous-00s-the-magic-and-delight-of-foxxxwoods-connecticut/" rel="nofollow">this game</a> in the comments. </p>

<p>NOTE: Not all the games are about <em>Keres attack</em> but please observe that this is a blog, not a theoretical book.</p>

<p>Another reason for including these links: <strong>Being FIDE master yourself</strong>, and <strong>those guys being IMs</strong>, you should have easier time understanding their moves and you should improve faster from those games.</p>

<p><a href="http://www.chesspublishing.com/content/4/jul07.htm" rel="nofollow">This article</a> mentions several <strong>key games</strong> for illustrating themes and ideas in <em>Keres attack</em>. To see them you need to register, but with some cleverness we can bypass this:</p>

<p>We know that the games mentioned were played in year 2007 or before, and know the names of the players and the <em>ECO code</em> of the opening. With these information it was not hard for me to find referenced games:</p>

<p><a href="http://www.chessgames.com/perl/chessgame?gid=1568694" rel="nofollow">Sokolov-Nisipeanu</a> ( notice that <a href="http://budapestchesnews.blogspot.com/2013/02/trends-in-sicilian-scheveningen-keres.html" rel="nofollow">this blog</a> mentions <code>e5</code> as serious novelty for Black as well-see the commentary <strong>bellow</strong> the diagram! )</p>

<p>Searching through the same database I found only one game between <em>Macieja</em> and <em>Kasimdzhanov</em> where they played <em>Keres attack</em> so <a href="http://www.chessgames.com/perl/chessgame?gid=1311010" rel="nofollow">here</a> is the link.</p>

<p>And <a href="http://www.chessgames.com/perl/chessgame?gid=1463108" rel="nofollow">here</a> is the last game.</p>

<p>These illustrate key ideas for black and ways the White copes with them-positioning of the rooks and minor pieces. For the original commentary of those  you shall have to get by yourself. </p>

<p>A good thing would be to compare the moves with the current theory, and to use strong engine to analyze the <strong>critical</strong> middle-game positions in order to reveal the mistakes players made. <strong>This should give you better insight about minor piece/rook positioning.</strong></p>

<h2>EDIT:</h2>

<p>There are no "typical plans" or "typical piece setup" in the <em>Keres attack</em>-only raw calculation and <strong>creativity.</strong> </p>

<p>You must be able to <strong>adapt to the every change in the position</strong>-which is logical-since these are open/semi-open games and that is the quality they require from a player. </p>

<p>Only closed/semi-closed systems can give you "typical plans/piece setup" which is logical when you think about it, since the closed nature of the position allows you to maneuver. </p>

<p>In open games things change rapidly, so to ask "typical plans" is pointless, especially in such a dynamic and sharp line like this. I would focus my attention on tactical sharpness.</p>

<p>The way I see it, you can use <code>g4</code> to force Black into making a concession on the king side and to grab more space. Then you should use <strong>your better piece coordination and space advantage</strong> to increase your initiative. Playing through the games I see this idea for White over and over. </p>

<p>This is the way I would approach this problem. </p>

<h2>END OF EDIT</h2>

<p>Unfortunately this is all I can offer at the moment, hopefully it will be enough.</p>

<p>Good luck and best regards!</p>
