Well, I’d say the books Projection of the Astral Body and Journeys out of the Body are good places to start. Alternately, if you’d like to try a legal “drug” to induce the phenomenon:
http://potionmixology.com
http://salviadragon.com
NOTE: they’re two different substances. The first is a “potion” that you mix yourself, the second is a plant called Salvia Divinorum (Diviner’s Sage), which can be made into a tea or smoked. Unfortunately, neither are free.

Also, if drugs aren’t your thing and conventional methods don’t work for you, you can always try binaural beat frequencies:
http://astral-projection.mind-sync.com
Also not free, but it works to a degree, and there’s a money-back quarantee. Sorry I can’t be of more help, I’m still working on it myself (and don’t really have money for the drugs, though I do have copies of both binaural files (There’s two that you can buy on the site, the link I gave you is the cheaper of the two).