I normally have issues falling asleep..I gotta keep the temp low, I like the a/c on while I sleep, an eyemask on so its completely dark, and wash my face with lukewarm water right before I lay down..that's my routine
Drink a tea or hot chocolate, or imagine myself into one of my usual sleep fantasies. I've done it ever since I was small. Generally, the scene is that I've been captured and confined in a space (so not moving around lots, which in conducive to sleep). Favourites are: kidnapped and locked in an old-timey carriage, in a zoo-like cage, a mermaid caught in a ship's hold (this one's real good coz I have to keep my legs together like a tail, haha). Anyway, I just think about how much I can't move and so in my fantasies I'm clearly somewhat bored so the main thing for the captured mermaid to do is sleep away the hours. Somehow it's often easier for me to fall asleep in a role than just as my sleepy self.
I've been plagued by this before, and it was always stress related. A coworker recently suggested watching TV, reading, etc (which is opposite what I'd ever heard). So lately I've been actually getting up to watch an episode of TV or read nonfiction (fiction gets me too excited by the storyline). If half an hour on the couch doesn't work, then I go back to bed and do like txymxy: I imagine my man is here, tucking me into bed with him, us curled up together.
Assuming it's not insanely hot (in which case I'm not likely to rest well no matter what I do), I find that either thinking up a new story to write later or thinking about sex actually puts me to sleep pretty quick - I've always heard that thinking about something pleasant is key! If I'm having trouble (say, stress, or I drank caffeine too late in the day), I might masturbate, read, or drink some warm milk (preferably with some vanilla coffee creamer in it - YUM!). In a real pinch, sometimes getting up and surfing the 'net for an hour or so will do the trick.