Astral projection is not facilitated through effort or practice but rather through allowing yourself to become one with the "state of being" most compatible with this "heightened" awareness.
It can only happen when you are in a relaxed state, without fear. It is a natural occurrence, but the mind will stop it unless you "become one" with your natural state. The best example I can give (and I know some people find this an odd analogy, but it is metaphorically accurate) is a male erection or a female's state of sexual arousal.
It happens on its own when the conditions are right -- and no amount of thinking or hoping will "force" it to happen and fears and tensions can keep it from happening.
This is a close parallel to the pre-conditions for "astral projection". You don't teach someone to "be more psychic" -- you help them remove all the clutter "between them" and their natural, intuitive state.