Don't be a pussy (i.e. don't be afraid to stick your head out). If no-one is shooting at you and you don't have anyone to shoot at, move. Keep moving up on them, shorten the field and it will panic your opponents.
Also, paintball is a game of angles.. you want the widest possible angle on your enemy as it will reduce the cover they have. This means, don't rush up the middle of the field.. stick to the edges and look in/across field.
Lastly, gun up! always have your gun up!
P.S.