I learned this one from a friend:
An important part of snap shooting is to not only be quick and accurate, but also know when to tuck back in. With your full setup, drill with another friend, while he shoots at you. You have no paint, but that's not the point. The point is to test/improve your paintball tracking abilities. Watch the paint coming toward you and only go back in right before you see one coming at your face. As soon as the paint passes by, come out again. Do this over and over...