All you have to do is fall asleep like normal, except maintain a very small amount of awareness. It's almost like falling asleep normally. It's best to do this when you wake up really tired, say in the middle of the night, so that you're already half asleep. The goal then is to stay in that state of mind by continuing to relax your body and mind, and half-drifting off. When you hit body paralysis, continue to do what you were doing before. Soon enough, you'll feel a sort of tug out of your body (at least this is what happens to me), and at that point you need to will yourself in that direction, all while maintaining your very low awareness. Then you'll enter the dream. I imagined myself in an underwater room, and it manifested.

Oh, and for me it seems like a continual decrease in awareness + deeper relaxation, but meanwhile still maintaining awareness.