user10601: Supposing my opponent has little time left and I have much more than him (e.g. 10 minutes to 50, or 1 to 5, or 20 seconds to 1 minute).
What are good strategies that take advantage of my rival's time situation?
I read this article, and I will quote this part which I liked:

When the opponent is in time trouble, Webb advocated the barrage technique which involves planning two or more moves ahead, and then playing them in rapid succession. The idea is to give the opponent little time to prepare for the second move, increasing the probability of that move being a mistake. Playing a barrage of moves does increase the chance of a blunder from the barrager as well, and the technique is inadvisable in a winning position where a player should focus on winning on the board.[2]

I agree that you should focus on your own game, but taking into account the opponent's time may help you. One idea could be to delay exchanges to make the game longer and make complicated positions on the board.
Edit: I'm playing blitz/rapid chess with times between 3 and 30 minutes, without any increment, and online.

user10233: "I'm playing blitz chess with times between 3 and 30 minutes, without any increment, and it's not over the board (it's online)."
a: That is not blitz.
b: Wikipedia does not qualify to give advice about chess.
The best advice you can get, and this I got from a GM (James Rizzitano), is "Play the board." By playing to your opponents time pressure, you put yourself in time pressure. Simple as that. A good move is a good move. 
The only time - the only time - this idea can work is if you are losing and you want to complicate the game to try and gain an advantage, as stated in the quote.
Otherwise, play good moves and do not change your thinking process.

user17: Find the sharpest, most complicated variation that the position (and your own ability) will support. Take a reasonable amount of time to do this, because you have it, and your opponent doesn't.
Once you've formed your plan, play it out step by step. Make your moves in natural tempo, let your strategy unfold, and let your opponent panic in time trouble.
A cautionary put out by another poster holds: This is not the time to "sit back and relax," and possibly let your opponent catch up. This is the time to play "hard," the hardest game you can possibly play, and hope that your opponent doesn't have the time to play it with you.

user9030: 
Do not play fast.

This is a common pitfall. He/She is the one who has to play fast, not you. Take your time and find a good move. Your opponent can't compete with you as he/she doesn't have enough time.

Do not simplify the game, make it more complex. 

Obviously, complicated positions are disadvantageous for the one who is in time trouble.

Don't think you won already.

You didn't, yet. If you sit back and relax, bad things gonna happen. Stay sharp.

user291: Don't try to blitz him by playing fast; now you both are playing without thinking much and you've lost the point of the time advantage.
In general, you should still just try to play the best moves. But if there is any general strategy, it is to avoid forced moves on both sides, so that he has more to consider on every move. Unless it is advantageous, don't start some sequence of captures or checks or an otherwise forced sequence, as he will be able to play a few moves in a row very fast. Keep your threats active and play quiet moves.
If he is really really low on time (like, under a minute), then while your clock is ticking he will probably be looking at a few of your possible moves and trying to come up with a response to each of them that he can play instantly. If you play a different, quiet, move instead, he is likely to waste a few seconds just trying to make sense of it before he can even formulate a good response.

10601: <p>Supposing my opponent has little time left and I have much more than him (e.g. 10 minutes to 50, or 1 to 5, or 20 seconds to 1 minute).<br/>
What are good strategies that take advantage of my rival's time situation?</p>

<p>I read <a href="https://en.wikipedia.org/wiki/Time_trouble" rel="nofollow">this article</a>, and I will quote this part which I liked:</p>

<blockquote>
  <p>When the opponent is in time trouble, Webb advocated the barrage technique which involves planning two or more moves ahead, and then playing them in rapid succession. The idea is to give the opponent little time to prepare for the second move, increasing the probability of that move being a mistake. Playing a barrage of moves does increase the chance of a blunder from the barrager as well, and the technique is inadvisable in a winning position where a player should focus on winning on the board.[2]</p>
</blockquote>

<p>I agree that you should focus on your own game, but taking into account the opponent's time may help you. One idea could be to delay exchanges to make the game longer and make complicated positions on the board.</p>

<p>Edit: I'm playing blitz/rapid chess with times between 3 and 30 minutes, without any increment, and online.</p>
 10233: <p>"I'm playing blitz chess with times between 3 and 30 minutes, without any increment, and it's not over the board (it's online)."</p>

<p>a: That is not blitz.
b: Wikipedia does not qualify to give advice about chess.</p>

<p>The best advice you can get, and this I got from a GM (James Rizzitano), is "Play the board." By playing to your opponents time pressure, you put yourself in time pressure. Simple as that. A good move is a good move. </p>

<p>The only time - the only time - this idea can work is if you are losing and you want to complicate the game to try and gain an advantage, as stated in the quote.</p>

<p>Otherwise, play good moves and do not change your thinking process.</p>
 17: <p>Find the sharpest, most complicated variation that the position (and your own ability) will support. Take a reasonable amount of time to do this, because you have it, and your opponent doesn't.</p>

<p>Once you've formed your plan, play it out step by step. Make your moves in natural tempo, let your strategy unfold, and let your opponent panic in time trouble.</p>

<p>A cautionary put out by another poster holds: This is not the time to "sit back and relax," and possibly let your opponent catch up. This is the time to play "hard," the hardest game you can possibly play, and hope that your opponent doesn't have the time to play it with you.</p>
 9030: <ul>
<li>Do not play fast.</li>
</ul>

<p>This is a common pitfall. He/She is the one who has to play fast, not you. Take your time and find a good move. Your opponent can't compete with you as he/she doesn't have enough time.</p>

<ul>
<li>Do not simplify the game, make it more complex. </li>
</ul>

<p>Obviously, complicated positions are disadvantageous for the one who is in time trouble.</p>

<ul>
<li>Don't think you won already.</li>
</ul>

<p>You didn't, yet. If you sit back and relax, bad things gonna happen. Stay sharp.</p>
 291: <p>Don't try to blitz him by playing fast; now you both are playing without thinking much and you've lost the point of the time advantage.</p>

<p>In general, you should still just try to play the best moves. But if there is any general strategy, it is to avoid forced moves on both sides, so that he has more to consider on every move. Unless it is advantageous, don't start some sequence of captures or checks or an otherwise forced sequence, as he will be able to play a few moves in a row very fast. Keep your threats active and play quiet moves.</p>

<p>If he is really really low on time (like, under a minute), then while your clock is ticking he will probably be looking at a few of your possible moves and trying to come up with a response to each of them that he can play instantly. If you play a different, quiet, move instead, he is likely to waste a few seconds just trying to make sense of it before he can even formulate a good response.</p>
