When firing your gun, if you don't already have a double trigger, you should use the middle finger. It enables you to fire faster, plus the other way is just old school.
Practice shooting when your not playing paintball. Have a friend or team mate throw a small box in the air and see if you can hit it while its moving. Do this from about 30 ft away and then have your friend move back and do it again. Another thing to do is to set up a soda can about 120 ft. away and lay on the ground and try to hit it.
Something that will help you out in the above practices are a good quality paintball. You don't want them flying in every direction. Even if you do buy the best, don't let them sit still in their box forever because then the paint sits and they become lopsided. This happens because the weight isn't distributed evenly inside the ball.
If the field has a lot of trees on it, that means it could be a long ball field. Meaning, people move from tree to tree and there isn't much cover on your flanks when hiding behind a tree, so everyone tends to stay back and shoot long shots at each other. Practicing shooting a soda can from far away would help you on these fields.
There's a reason why most everybody wears camo: To not give away your position. There are times when you should stay in one spot and wait until the perfect opportunity arrises to fire at the enemy.
