I have trained Soldiers in CQB for real missions, here's what I can tell you. I will be squashing a few of the opinions offered here. No offense intended.
The first thing you need? Practice. Before the day of the game. Get the guys you are going to play with and walk throught the drills. There are a million ways to move through a building or clear a room and none of them are "random".
I say walk because you don't run during CQB. You don't dive or roll or do back flips with a pistol in each hand. Forget the movies. When I say walk, I don't mean that you saunter, meander, or mosey. You move with a purpose. That applies to everything you do.
CQB is a contact sport. You will touch and be touched by your team mates. You don't need to ask "are you with me?" when a firm grip on your should literally says "I have your back".
CQB is an excersize in commitment. By that I mean that when you commit to an action, you follow through. You don't stop because you see an enemy, you don't pause in the doorway because you turned the wrong way. You complete the action.
CQB embodies three things. SPEED, SUPRIZE, AND VIOLENCE OF ACTION. After you clear your first room, you will lose suprize so you need to make sure you are solid on the other two.
Do not bunker down. CQB is dynamic, fluid, always changing. Once your location is pinned down, the enemy will come and get you.
Cover your buddy. You should not have to be told to cover the window as you go past or your buddy's sector of fire while he reloads. You should be aware enough of your surroundings to just do it. The same applies to guarding the rear. Do not walk backwards, EVER. You don't step into unknown space.
Do not try to be "stealthy", you're not. Communicate with your team, loudly and clearly. You don't need radios, you should never be out of talking distance.
Communication. It's a small area, everyone knows where you are anyway. There is more to be gained by clear communication than lost by the enemy knowing your whereabouts. That doesn't mean sit back and have a conversation. Verbal comms are fine but use it efficiently. Team leader gives and order, you confirm and execute.
If you are going to carry a sidearm, learn to use it. Practice transitioning from your rifle and back. Learn to holster yout pistol quickly and without looking at it.
Get your kit set up for your use. Make sure you can reach what you need to. Are your mags easily availible? All of them? What do you do with your empties? Have a plan and follow it.
Do not shoulder sling your rifle unless that is your only option. Get a length of paracord and a carabiner and make a field expedient one point sling. Clip it to your shooting shoulder and tie it to hang your weapon close to your chest. That way you can just drop it when you go for your pistol.
Don't "wear mostly black", that has nothing to do with anything. Camo is not an issue for CQB and even if it was, black has no camo properties at all.
Grenades, flash bangs, etc. These toys can help but they won't do anything for you if you don't master the fundamentals. Just like a $2000 scope won't make you hit your target if you're a bad shot.
Shoot center mass. No head shots. First off, it's rude and second, we aren't here to hurt anyone. The torso is the biggest target. That being said, shoot whatever the enemy presents to you, if it's just a head and a gun, go for the head.
Trigger control. Learn the art of the controlled pair. Semiautomatic, two deliberate shots. If it's worth shooting once, it's worth shooting twice. You only do bursts for suppression.
That's what I have for now. I know I didn't go into specifics but you need to do your research. This isn't something that can be learned by reading. Walk through the drills, figure out what works for you, and do it the same way every time. Consistancy is the key."