All the other peeps are giving sound advice, I read the books of Robert Monroe, supposedly one of the best known AP'ers out there. His book "Adventures beyond the body" is a very informative and entertaining read, and in fact I find AP easier when I've been doing lots of reading and feeling out of the subject. Be warned, if you are unprepared for high weirdness it may not be something you want. In the end my AP practice sublimated into a regular lucid dreaming pattern, because direct AP techniques were bringing me face to face with my own demons. I ended up in a kind of "armed robbery in hell" scenario where I was battling evil constantly, and it became really draining. It wasn't until I realised these thing were as much inside me as outside that I began to mellow and have fun. If you meet demons or "evil" entities they find warmth and love much more unbearable than violence and anger. Give them funny hats and funky music to dance to, they really don't like that.
I can see the sense in buddhist notions of spiritual purity when dealing with the astral plane, as any emotional vibration will draw you to that emotional plane. Try lucid dreaming techniques first, as AP seems to me to be a high end, high frequency version of this mental state. I'm no expert, but I have been trying for years to make a difference on the astral plane and lucid dreaming is far more organic and empowering, and is pretty much the same technology. Remember to have fun and use LOVE as your basic vibration and you'll be fine.
Sabretooth, that was the most striking thing about my first experience, the actual feel of the etheric body out in the world, air and light have very different effects on the subtle body. Electric lights hurt my etheric eyes!