never have your rifle out unless you're taking the shot. Get someone to watch your back, if possible. You can kill people with your pistol, but it's better to use it to make the other person take cover as you escape. An assault rifle can hit you, don't me a moron.
Most of all, don't stay in the same place for too long, especially in buildings. You'll want to get onto hills or someplace people don't normally go. If someone is serpentining towards you, don't try to hit them because you're forgeted once they get into a position where they can shoot you. Don't piss people off by camping, they will lose all other priorities and try to kill you by any means necessary. You can't kill tanks. If you knifed someone who was where you wanted to be, they are probably going back there to find you. Bring a medic if you can, medics have good firepower and they can revive you quickly, they can also watch your back so no one sneaks up on you.
