Another couple of points.
Squeezing the trigger has been mentioned. At least as important is the follow-through. You can't believe how far you can miss a shot with the reticle in exactly the right spot, if you get excited and get jumpy on the trigger. especially when your air starts to run out, because you are of course holding your breath.
Stance. What is your weight distribution like? It should be slightly on the front foot.
Also, concentration! You have to focus on making the shot. Not be thinking about missing.
