There are several books by guys like Ferguson, Asbel and others. Get them all. Try all methods, and just keep shooting. After a while, things will start to click for you. When I am in practice, I know that my arrow will hit the target when I reach my anchor. Then the release just happens, almost without a conscious effort.

Your brain will register the arrow's flight, or trajectory, to the target. With repetition, this becomes second nature. Concentrate on form rather than groups.

Shooting can be so much fun that it is easy to shoot too much at a session, especially for a beginner. That's where you can get in trouble, because as your form breaks down from fatigue, you are reinforcing bad feedback.