it's kind of hard to teach. But I would be happy to tell you how it worked for me.
I meditate first until I am at ease, calm, and colected, then I lay down just like I am going to bed, focussed on astral projecting. then as I drift asleep, I let myself go onto the astral realm.
Essentially, it's like just falling asleep, but you push yourself onto the astral plane. I hope this is of some help