What's your policy on downs?
I used to try to revive people all the time, not checking my surroundings. Almost always I ended up reviving, then getting killed, then my teammate gets killed, too.
Or when I was down, I'd crawl towards teammates during battle. They'd get exposed and killed. Oops!
Nowadays I only revive under cover (and even sometimes I forget to look behind), and don't crawl towards anyone if the enemy is around.
Also, the sprinting while the rest of us is crouch-walking.