Reasons for hitting left (DAMHIK):
(Assuming you are a right-hand shooter)
1. Shoulders pointing to the left of target
2. Not keeping slight bend in bow arm elbow
3. Dominant eye not centered over arrow
4. Arrow too stiff or strike plate too far to left
5. Your head moves when you come to anchor and pushes your string hand to the right, which moves the shot to the left
6. You are not using a solid anchor against your face, and thus the back of the arrow is too far to the right, throwing the shot to the left
7. Not focusing exclusively on target, and the arrow is catching your attention in your peripheral vision. The arrow point will naturally be to the right of the target in your peripheral vision, and you are unconsciously moving the point over toward the target, thus moving the impact to the left
8. Not coming to full draw. Your string forearm is pointing to the left of the target when you release
Believe me, I've tried 'em all, and they all work pretty well if you want to shoot left....