Usually, I just close my eyes and kind of go into "manual mode" for dreaming, meaning I just picture whatever comes to mind and just start running images through my head, be it something I'm thinking about that I experienced recently or just doing some creative thinking. The trick for me, anyways, is to get to a point where I'm no longer conscious of my body and I'm pretty much day-dreaming. Thinking of tranquil things, like imagining a walk through the woods or along a beach, usually helps, too. Just let your imagination wander as you take in the scenery and kind of lose yourself in the moment. It might take a long time to get to sleep, but the goal is to get your body to relax and not cling to any serious thoughts. The more you focus, the harder it is to drift off.