Second self technique:

I think this astral projection technique is most common as it is taught in many books and is relatively easy. Especially if one is profficent at meditation and visualization.

1. Enter a state of meditation while in a position comfortable to you. Chances are if you lay down you'll fall asleep! Which can actually produce results if your mind can be focused on intentions to AP.
2. If you're not asleep by now ;-) vizualize a white light originating in your solar plexus- about two inches below your sternum. Optionally you can do this through your third eye. Located an inch high and inbetween your eyes.
3. Let it start as a white dot and let it Slowly grow into a sphere that surrounds your body.
4. Lets this sphere of light become a siloette of your body.
5. This is probably the hardest step and will take several tries to get the hang of it. Picture this body of light hoovering just above you. As though you could reach out and touch it. Don't try to with your hand, but your mind. Try to get your consous mind to become one with the body of light.
6. You will know if you are successfull when you feel as though you're floating. Like on a boat in the ocean. This sensation alone may be enough to kick you back into your body. Which is partially why I stress learning the skills of meditation. Feel yourself drift for a period of time to adjust to the sensation.
7. Focus on being outside of your body, floating. Best to start simple here. Mentally open your eyes so that you are looking at yourself. Notice that your body is safe and undisturbed.
8. Time to explore. Once you have made this far continue to notice what surrounds you. A good way to experience this is prior to attempting astral projection throw a deck of cards on the floor so that they are randomly strune about. Then begin to meditate and AP. Once out side of your body look for the cards. Try to notice which ones are face up. Additionally you can look about your surroundings. But its best to get good at looking around your room or area before you go out into the world. After about several days of successfully being able to get out of your body and explore your area then you can step outside. Use the door please ;-). Kidding you can try to go through a wall. Or explore the inner space of a closet. Or fly out a window. Best to do things within your skill level.
9. Re-entery; Return to your area and find your body. Get to the same picture where you're looking face to face with yourself. See your body glow with light and gentally fall back down towards it until your can feel yourself no longer floating. Once your no longer floating visualize that glowing sphere return to your solar plexus or third eye and watch it disappear into.
10. Start breathing deeply and relax for a few monents, congrats you've just left your body. It is best to end this by recording your experience in a journal while having a snack. A small meal will help your body ground your astral body and releive your psychic mind of any stress from being out of its physical body.

Again for beginers don't expect much the first few times around. If you find yourself disturbed in the initial attempt to leave your body such that you loose focus start over from scratch or try again another time. If you are successful what you can expect will be much like a dream. You'll notice that you are aware, at least semi-aware and able to partially control where you go and what you do. The more you pratice the better, easier and faster it'll be to AP. The first few times you might not be out much more than a few seconds or maybe minutes. Don't try to stay away from your body too long. Your perception of time will be distorted, like in dreams, but its best to not remain out of your body more than a half an hour until you are confident in your abilities. Like I said the mind used in this way is like a muscle. So by remianing away from your body too long you are putting strain on your mind which will make it harder to recuperate and symptoms like a mental block can appear. Again a mental block can be like litterally having difficulties focusing on anything. Head aches, and dissoreintation.