Here's how I always try to explain it: relax you drawing hand so the fingers just have enough tension to hold the string. I find it helpful to practice with bow vertical; seems easier to develop back tension this way. Bring bow arm up; imagine now that there is a string attached to the tip of your elbow (drawing arm) and string is attached to bow string also. Visualize drawing the bow by using back muscles to push your elbow back, and the bow is drawn back only by the string that runs from your elbow to the bow string. Don't incorporate bicep, shoulder, or hand/finger tension to draw the bow, only think of drawing it with the elbow and the imaginary string that runs from elbow to bow string. At full draw, think of pushing the elbow straight back away from the target as your fingers relax; the string will explode from your hand and the bow will "fire" itself. If you do this right, your bow will recoil straight at the target and your string hand will recoil straight back and into your shoulder. This is, in truth, what the Formmaster training aid teaches you to do, but it uses an actual string that runs from your elbow to the bow string.