After making every conceivable mistake, and inventing several new ones, I have concluded that the following is necessary for me to be able to shoot accurately:
1. Proper body allignment, such as illustrated by Terry's clock.
2. Proper back tension, such as discussed by Rod Jenkins in MBB III.
3. A surprise release, such as taught by Rick Welch, Rod Jenkins, and others, where there is no conscious opening of the fingers to release the arrow.
All the other differences, aiming methods, anchors, etc., taught by people are just refinements of the basic theme, which might work better for some people than others. But the three items above seem common to any method of accurate shooting.