Relaxation
You must learn and master, a full body relaxation exercise. If you know one already it can be adapted to suit. Here is a very simple one:
Sit, or lie down, and relax. Starting with the feet, tense and relax them. Continue this with calves, thighs, hips, stomach, chest, arms, neck and face until your whole body is deeply relaxed. Go over this a few times, making sure your muscles stay relaxed.
Note: Deep physical relaxation is the key to bringing on the trance state, i.e., deep relaxation CAUSES the trance state. Once you are in the trance state, projection on the astral body is relatively easy.