First off, no offense to the above posts but you should not open your hand, the bow hand should be relaxed, not gripping the bow but not forced open either. When your bow hand is relaxed, the fingers will naturally curl around the bow but not grip the bow. Forcing your hand open is unnatural. Second, no one can hold dead on steady. It's natural for the pin to float on the intended target. The key to consistant accuracy is a combination of form, muscle rememberance, concentration, consistancy and follow through.

Form: Proper form is essential. Improperly holding a bow can throw you off and consistancy comes into play within this equation as well. When you learn proper form, and you consitantly hold the bow the same way, shot after shot after shot within the muscle rememberance, you can practically close your eyes and hit your mark. That's why golfers take a practice swing prior to a shot, the muscles will remember what just happened and rerun that same swing. I showed this recently at a pro shop open house. I consistantly hit a 1" circle on a video target with several new bows without sights. When asked how, I simply answered muscle rememberance. My first shot, with proper form and relaxed shooting position created the target. All the other shots where simply shot the same way, without aiming. My body simply repeated the same process on each shot.

Now when throwing sights on a bow and aiming, concentration comes into play. Your body already knows what to do, now you need to make your mind control where the shot is suppose to go. That's why in ZEN archery, you'll learn mechanically how to shoot bow and never worry about the target. A good way to practice this is remove your sights, get up close and let your body learn the mechanics of shooting. Once you think your body is ready, put your sights back on and see if your mind will allow your body to do it's thing and your mind simply points the bow in the right direction. Once your pin is on a target, don't fret that it moves around the target, simply allow your body to trigger the bow all the while your mind is concentrating on the target. Allow the shot to be a surprise, don't force the shot, even if your floating, you'll be surprised how many times your pin will be off when you think the bow goes off and the arrow will find it's mark.

Follow through....again this comes in not forcing the shot. You can't hold dead on, the pin is going to float and when the shot goes off, allow the bow to freely jump. Don't force it still.

When you find consistancy through good form and concentration, your groups will come.