Well one thing, of course, is dreaming. Sometimes you'll remember dreams. But something weird happens. When you remember a dream, you also notice that during the dream it'll be real, like you're really there. Then you wake up and recall the memories of it. But if you have no memories of a dream when you wake up, you'll notice that you never seemed to live the dream, when you actually did.

Anyway, normally you are not in control of your dreams. Some people are, but I'm not. Being able to realize you are dreaming, and then gaining control over your dreams is a great way to practice astral projection. Lucid dreaming alone can be a great experience and I will have some links for it. I've only done it twice so far.

Another method to astral projection is to keep your mind awake as your body falls asleep. Since I haven't been able to project yet (getting close), or at least been aware of doing so, I won't explain how to project. But I will of course list articles and links to lots of information. Enjoy.

Articles

Robert Bruce's treatise on astral projection. Excellent read.
The Astral World
Flake's Teachings About AP

Links

Astral Society
Astral Pulse - Robert Bruce's site
Saltcube - Metaphysics You Can Test For Yourself
Mysticweb
Astral Voyage