Run motherf***a run!!!!
That's what I do. Although I kind of expect my teammates to watch my back. Takes too long to watch everywhere. Once in a while I get shot in the back, but usually if I get the flag, I'm gonna make it. I get pissed when your teammates don't even make an attempt to cover you. I usually will, run to my teammate who has the flag, and do my best to take out any enemies following. Have even jumped in front of bullets to try and take the sacrifice for the team, but that is usually only when I run out of ammo, and am too close to do anything else.
Seems to work ok for me.
Running Strategies: For like warhead, I'll cover my teammate as they run through the sewers as it seems that people like that route quite a bit, and then after another teammate shows up to cover them, I haul ass for the flag. So that by the time that they get back with the flag, it has just appeared and I snatch it up, and I'll take the bridge from bravo's flag back to alpha as fast as I can. The longer that you lolligag, the more opportunity to get shot and killed.
Most maps I do about the same, except for junk flea and I don't really care for junk so I don't play it that often. When I do, I just make an attempt to be really fast. I use the light vest and my green beret, for a total +12 speed. Makes me pretty quick, not as fast as the assholes with the bandana, but pretty fast. If I've got a clear run, I can make it. That's it, I run, I don't screw around I get there and get it done, so I can go back to killing the enemy and try to take the flag.