I like those tips above, and would only add a bit to the one about shooting from a dominant position. Be sure to get in the habit of not being in the same place every time your opponent pops out to snap shoot. I love it when some kid hangs out the side of a bunker waiting for me -it's the easiest snapshot in the world (as if any of them are easy). If I'm posted on someone, I'm changing my location every time the guy pops out. If I was standing, I drop to a knee. If I was kneeling I stand, etc. That way when they come out you have an extra split second while they find you again.