I agree with pretty much everything everybody has said so far. I've had the problem before too. The first thing you have to accomplish is to be able to draw to full draw and hold without releasing the shot. People can generally draw and hold if they don't intend to shoot. If you can't do that, then I can't help you.
Assuming you can do that, you have to figure how to do the same thing if you intend to shoot. These are things that have worked for other people:
1. Draw without the intention of shooting, and don't give yourself permission to shoot until you have good alignment at full draw.
2. Draw to full draw without focusing on the target. Instead, focus on the riser or the point of the arrow. Before you shoot, shift your focus to the target.
3. Close your eyes as you draw the bow. Open your eyes after you feel that you are at full draw in good alignment.
These measures are more extreme as you go up the list. Use the least extreme method that will work for you. The problem is, each of these makes you drift more off target than the previous one. For example, if you close your eyes while you draw, when you open your eyes you will find that you have drifted off target, and you will have to move your bow arm to get back on target. It really destroys accuracy to move your bow arm at full draw, but use it if you must, because the first thing is to get to full draw without firing prematurely. In fact, the thing you have to convince yourself of is that you will NEVER fire the bow until you are at full draw in good alignment on target. Once that is solidly ingrained, then you can start working your way down the list.
Start this now. Unless you address the problem, it will only get worse with a new bow.