user881: Some people who I play always play the symmetrical variation, and I don't know how to play it for white.
[fen ""]
1.d4 d5 2.c4 c5


user72: The symmetrical defense is my favorite, here is how games with me playing as black usually turn out:
[FEN ""]

1.d4 d5 2.c4 c5 3.dxc5 d4 4.Nf3 Nc6 5.e3 e5 6.exd4 exd4

This line of play of course requires white to play 3. dxc5: it is quite a common variation I find. White cannot defend the c5 pawn effectively and black has a clearly dominant position including a passed pawn. A word of caution: in this position development of your pieces is more important that material equality so if white chooses to defend the c5 pawn simply allow him and develop, building pressure elsewhere or even on the pawn itself. 

user924: It's really unknown, I've never seen it actually played except for maybe one or two internet blitz games out of ten thousand. But I've looked up some lines for you.
You play 3.cxd5 and now black needs to decide what to do.
The symmetrical 3...cxd4 4.Qxd4 followed by e4 just loses a pawn.
3...Qxd5 allows white to chase the queen, getting a lead in development:
[FEN ""]

1.d4 d5 2.c4 c5 3.cxd5 Qxd5 4.Nf3 cxd4 5.Nc3 Qa5 6.Nxd4

So black plays 3...Nf6. Now a thing like 4.Nf3 cxd4 5.Qxd4 Qxd5 stays completely symmetrical, but white can play 4.e4!.
Fundamental Chess Openings gives two lines, both a bit better for White because of better development:
[FEN ""]

1.d4 d5 2.c4 c5 3.cxd5 Nf6 4.e4 Nxe4 5.dxc5 Nxc5 6.Nf3 e6 7.Nc3 exd5 8.Qxd5

and
[FEN ""]

1.d4 d5 2.c4 c5 3.cxd5 Nf6 4.e4 Nxe4 5.dxc5 Qa5+ 6.Bd2 Nxd2 7.Qxd2 Qxc5 8.Na3


881: <p>Some people who I play always play the symmetrical variation, and I don't know how to play it for white.</p>

<pre><code>[fen ""]
1.d4 d5 2.c4 c5
</code></pre>
 72: <p>The symmetrical defense is my favorite, here is how games with me playing as black usually turn out:</p>

<pre><code>[FEN ""]

1.d4 d5 2.c4 c5 3.dxc5 d4 4.Nf3 Nc6 5.e3 e5 6.exd4 exd4
</code></pre>

<p>This line of play of course requires white to play <code>3. dxc5</code>: it is quite a common variation I find. White cannot defend the <code>c5</code> pawn effectively and black has a clearly dominant position including a passed pawn. A word of caution: in this position development of your pieces is more important that material equality so if white chooses to defend the <code>c5</code> pawn simply allow him and develop, building pressure elsewhere or even on the pawn itself. </p>
 924: <p>It's really unknown, I've never seen it actually played except for maybe one or two internet blitz games out of ten thousand. But I've looked up some lines for you.</p>

<p>You play <strong>3.cxd5</strong> and now black needs to decide what to do.</p>

<p>The symmetrical <strong>3...cxd4 4.Qxd4</strong> followed by e4 just loses a pawn.</p>

<p><strong>3...Qxd5</strong> allows white to chase the queen, getting a lead in development:</p>

<pre><code>[FEN ""]

1.d4 d5 2.c4 c5 3.cxd5 Qxd5 4.Nf3 cxd4 5.Nc3 Qa5 6.Nxd4
</code></pre>

<p>So black plays <strong>3...Nf6</strong>. Now a thing like 4.Nf3 cxd4 5.Qxd4 Qxd5 stays completely symmetrical, but white can play <strong>4.e4!</strong>.</p>

<p><em>Fundamental Chess Openings</em> gives two lines, both a bit better for White because of better development:</p>

<pre><code>[FEN ""]

1.d4 d5 2.c4 c5 3.cxd5 Nf6 4.e4 Nxe4 5.dxc5 Nxc5 6.Nf3 e6 7.Nc3 exd5 8.Qxd5
</code></pre>

<p>and</p>

<pre><code>[FEN ""]

1.d4 d5 2.c4 c5 3.cxd5 Nf6 4.e4 Nxe4 5.dxc5 Qa5+ 6.Bd2 Nxd2 7.Qxd2 Qxc5 8.Na3
</code></pre>
