I'll try and make this as short and clean as possible due to the fact I know most of you are just interested in practical. :)
First practice how to relax you're whole body, every single muscle, practice this every night. You should also practice concentrating on 1 goal. Concentrating on what you're doing on the day, ignoring thoughts and day dreams will help you concentrate on Astral Projection and also may you meditate much more sufficiently.
As usual, Will power is really important, you have to want this, you have to be fully concentrated on what you want.
Once you've done all this, you can begin practicing AP.
There are many techniques out there, but the most effective one I've come across is the heart beat technique.
Lie on your back, with your hands on your side, body straight. relax every part of your body, face, tongue, arms, shoulders, etc. Concentrate on your heart, feel every beat. And as you continue to do this, you'll notice the beats will become more intense and louder. You may feel some electricity-like feeling on either your arms or legs.
DO NOT be distracted by these side effects, continue concentrating on your heart, and that's when you'll begin to lift.
Be sure to ALWAYS keep your mind clear when doing this, clear your thoughts.
The furthest I've been was just lifting half-way and snapping back again. And trust me, the feeling of snapping back for the first time is frightful hehe. Literally feels like you're falling.