HOW TO PLAY BLITZ
Blitz chess is slightly slower than bullet, but faster than standard. Most people who play blitz play a 3|0 or a 5|0 just because it's fast, but you actually can think about your moves. Anyways, here are some tips on playing blitz.
1) DO NOT RUSH YOUR MOVE! Unlike bullet, you can actually think a little bit in blitz. Most of the time when I play blitz (like legit against people not like trolling kzhang), I have my premoves turned off. Since premoving on chess.com is unable to be cancelled, if you premove in a blitz game, your opponent will have a chance to make a better move and when it's your turn, your piece moves right into a square where it can be captured.
2) DO NOT THINK TOO DEEP! Although blitz chess is not as fast as bullet, it does not mean you have to think very carefully like how you would in a tournament. Instead, look for quick tactics that you can apply to the current position and use them. Don't think about long term strategy.
3) ALWAYS WATCH YOUR TIME! Just because blitz is not as fast as bullet does not mean that you should not watch your time. If you move too slowly, you may not have enough time to checkmate your opponent. Usually when I play blitz, I always make sure my time is within 10-20 seconds of my opponent's time.
4) OPENINGS: In blitz, try to play an opening that you usually play in standard chess. If you're a defensive player, play defensive; If you're an offensive player, play offensive. The most important part of the blitz opening is not to mess up and hang pieces.
5) THE MIDDLEGAME(if ahead on time): The middlegame of blitz games are the most important part of the game. Most of blitz games will have a very tactical middlegame with lots of traps and stuff. Try spending more time on the middlegame of the blitz game to actually think a little bit about the position.
6) THE MIDDLEGAME(if behind on time): If you happen to be behind on time in the middlegame, don't think too much about your position. Yes, you should think about it, but just look for quick weaknesses in your opponent's position like forks or pins and take advanage of them. Also, buying time with checks in open middlegames can also help.
7) THE ENDGAME: Most blitz games, unlike bullet games, have an endgame where you can actually think about moves. In a blitz endgame, both sides of the board usually have about 30 seconds to 1.5 minutes left. When you get to a blitz endgame, it's usually all about the pawnworks. Try sticking your king in front of your opponent's pawn to slow the pawns down, and also protect your pawn at the same time. I actually don't have that much to say about endgames, cuz well in the endgame, I just use my instincts. -_-
Hope this helps :)