Count breaths until you feel you are getting close to sleep. Normally this will happen when you find yourself losing count a few times, or having stray dream-like thoughts entering your counting. Once this starts to happen, stop worrying about your breaths and your body, and counting. Think of a vivid recent memory. Something tactile, involving movement, touch, speed, ect. For example, you could imagine running down your street, and jumping over a fence. Try to get some extreme movement in there, such as falling, jumping, or rolling. Something where you feel it in your gut, like a rollercoaster. Use a memory so there is no work involved. It is not a conscious and forceful visualization. It is something that is already in your mind.

Run this memory / visualization over and over in your (now foggy) mind until your dream body starts to feel convincing and real. It will start as a daydream, but should take over if you keep at it. Keep your dream body moving and interacting with your surroundings.

Don't worry if you ping-pong in and out of reality a bit. Your attention might be divided between your body in bed and your dream body. You might have to start counting again if you find yourself getting too lost in your thoughts. You might get some on-and-off vibrations and sleep paralysis type symptoms. Don't worry. You haven't missed your chance. You will bounce around for a bit. Just keep doing what you are doing, and eventually the dream will take over when you hit a REM state.