Aim small miss small. Just like in the movies. A shooting instructer once told me to pick a spot to aim for. Then pick a hair in the spot I aim for. then aim for the center of the hair. Thats not possible most of the time but the message is to consintrate on that spot and nothing else. Clear your mind of everything else. Sort of look the bullet home. Next would come confidence which only can be gained by a lot of shooting. You must get to the point where you can know where that bullet will hit every time. You may not be able to avoid running shots but learn first to hit the standing shot. A miss by several inches on a still target can turn into a miss by several feet on a running target. Good hunting