Here I will list various CQB tips that I've figured out just playing at my local CQB area. I've played close to 12 hours total playtime so I have a good understanding of different tactics. If you have anything to contribute, post it below and I will add it.
- Watch where you are stepping, you don't want to be tripping left and right.
- Don't run, same as the previous, you don't want to fall while doing a rush, fast walk instead.
- Don't camp, it is annoying to the other team and it makes you more likely to get hit as people know your location.
- Don't be afraid to rush. I see a lot of new players staying back and camping and not rushing. Rushing is a great way to catch your opponent off guard and get some quick kills when they're not expecting it.
- Communicate with your team. If you see an enemy in the left corner of the room, then shout "Enemy, left corner!". Obviously don't shout if you haven't been seen as you don't want to give away you/your team.
- Move quickly and quietly. Don't be really loud, make sure your gear isn't making sound as you move so you don't give yourself away. Move quickly to get an advantage over the enemy as he probably won't realize you're moving in.
- Use the mercy rule. If you get really close to someone, use the mercy rule. I can count the scars on my arms and hands from new players shooting me point blank cause they didn't know the mercy rule. It sucks for the guy getting hit.
- Identify yourself as a teammate if allies are unsure if you are friendly or not. If you come around a corner and a teammate suddenly aims at you. Just say "Friendly" or wave.
- Check your corners. A technique I use for corners is quickly pop my head around the corner, take a quick look, and pop back in. I do this whole thing in about 3 seconds, be quick 'cause someone might be waiting on the other side.
- Always check doorways and chokepoints for booby traps.
- When entering a room or corridoor, don't all just stand there. Clear it out.
- Think before shooting. Don't shoot your teammates, if you see someone, make sure that person is an enemy before shooting and don't shoot at everything that moves.
- Don't unload on people. Usually one or two shots will do it (depending on what the other person is wearing). It sucks to have someone spray them point blank, so don't do it.
- If you shoot someone and s/he isn't calling their hit, feel free to unload on them until they do.
Rushing - This is basic, basically consisting of moving in an a enemy location quickly and quietly. This is a great tactic that takes the enemy off guard and is usually successful, especially against new players as they don't expect it.
Flanking - This is also basic, while in a firefight find a way around the enemy and get them from behind. This requires you to move quietly so the enemy doesn't realize as to what you are doing.