Here's a few tips for the beginner paintballer to help your performance on the paintball field...
1.  When you're hiding behind a bunker; if you decide to peek your head out to survey the field, move to a new location the next time you decide to look around the corner.  Sticking your head out of the some place twice is like begging to get shot in the face.  Try to make it so everytime you peek your head out, it's in a different spot.  Never stay in the same place for too long. A moving target is tougher to hit than a stationary one.
2.  Try to consistently keep your eye on all elements of the field in front of you, not just one object.  Many players become so obsessed with eliminating a particular opponent that they don't' notice another opponent  sneaking up on them.
3.  Keep track of your own teammates so you don't tag your own guy or become a victim of friendly fire.  Make sure you're aware of everyone's jerseys/colors (your opponent's and your own team's) before you start the match.  Maintain good lines of communication with your teammates.  Each member of your team should be adept at everyone else's positions in case you need to switch at the last minute. 
4.  Don't try to be a lone ranger out there and do everything yourself.  If you feel that you are in need of help, don't be afraid to ask for it.  It should go without saying too;  if your teammates call out for help, be there for them to provide backup or cover.
5.  Don't take shots at an opposing player until they get within elimination range.  By shooting at targets that are too far away, you will not only waste all your paintballs, but you might also possibly give away your position by making your location known.