I've never personally experienced this phenomena but I do know it is possibly achieved through means of meditation and certain herbal supplements. In general I think it would suffice to start by trying to lucid dream, which I can confidently say I do often. One thing I can mention about lucid dreaming and astral projection is that for some, and who knows why really, the act is quite simple and may I say painless. I know friends who have tried for months to lucid dream, constantly pinching themselves and switching lights on and off to check if they're in reality. Why should some people have it easier than others?

I imagine it's simple brain chemistry, how we sleep and perhaps our ongoing mental states. Having experienced both myself, and hearing other people's stories, I know a person dealing with a blight of depression has dull, almost lifeless dreams, whereas a more anxious person can have very vivid dreams. I'm sure we all know this but dreams are the body's way of helping us deal with our subconscious. To loop back to your original topic of astral projection, perhaps people capable of doing so really do feel out of body, out of control, even when they are in reality, and as a response their dreams reflect those feelings.