I always ask myself if I am hunting or being hunted. If I can't see anyone and I'm just wandering around I usually feel like someone is hunting me . . . that's bad. If I catch a glimpse of someone running I try to anticipate where they are heading, like a weapon or sniper spot, and then cut them off on the way. Let the others come to you rather than running around in the open the whole time.
Anther good idea is to watch for bullets streaming or smoke grenades going off and flank toward where they came from. If you see someone bleeding out on the ground don't run up and try to steal the kill, wait for the killer to come up to them and then toss a grenade between them both. Then you curb stomp two people. It's a lot easier said than done, but it's all about strategy. Working as a team is alway better than being on a team and working basically alone. If you have a newbie on your team hang back and follow him. Guaranteed he is going to draw fire soon from others and get himself killed, but in the process he will draw the enemy toward him while you flank. If two of you are crouched behind the same wall or box you are as good as dead. Once in a fire-fight don't just exchange fire, it's 50/50 odds. Instead wait until they crouch behind cover and then use smoke grenades to move laterally in opposite directions than your team mate. One of you keep him shooting at you from the original location while the other circles for an exposed shot. Eventually they will realize that they are exposed and their only chance is to either charge at you or run for it, but their odds of surviving at that point are slim if you both move in on them. Always try to start a fight when you have 2 against 1. Take turns getting kills and watching each others back.
Best case scenario is to pin one guy down with fire while your team mate moves to the side and uses the hammer of dawn.
Realistically there are so many kids out there that play this game online without parents monitoring them and they get so good at how to win that normal gamers have to work together to kill them. It sure is fun to curb stomp them though.