For the past 6-8 months, I've had bouts of INCREDIBLE difficulty falling asleep. Most of it due to emotional/psychological nonsense going on in my life. No big, major things of course, but enough to sometimes "keep me up nights, thinking".
That's my personality anyway: I'm a HUGE "what if..." and "would've/could've/should've" person as it is, so...
Honestly, this is how I fall asleep (just stumbled upon this recently): I don't drink sodas after 4pm (unless sleeping isn't my main concern) and I set my alarm clock and simply grab my ultra-hard (get your minds out of the gutter...jeez) CROSSWORD BOOK, and turn to a puzzle I haven't started yet and simply start doing it. Something about it, while lying down and tucked in, completely lulls me to sleep, and right before I know I'm past that point of no return, I'll put the cap back on my pen, lay the book and pen on my night stand and, with my last ounce of wakeness, flip off my lamp. I fall asleep immediately.
Usually 15-30 minutes of this "crossword treatment" is enough.
On really tough nights (or when I'm not in a crossword mood), I'll take 2 Tylenol PM tablets. Not a true sleeping pill (I only do it about twice a month, maybe three times tops), but within 30-45 minutes of taking them, I get a nice, pleasant drowsy feeling and it helps me stop thinking and worrying and wondering and replaying this conversation and that argument and all the bullcrap I often find myself going over and over.
I think the key, in short, is to find something flat and neutral to occupy your brain with (so that you're not thinking about work, relationships, bills, errands, etc.). But that distraction has to be something borderline boring enough so as to lull you into Yawn City.
In other words, no video games, "Die Hard" viewing marathon, etc.
Cool thing I've been doing lately also is setting the sleep timer on my TV for about 30 minutes, then find a channel with a stand-up comedian or sports highlights. I don't watch them (I turn over, close my eyes and bundle up), but hearing something funny or non-upsetting/non-offensive like a comedian or sports highlights seems to settle me down and I sleep well. And because I've set my timer, my TV will click off in half an hour or so, so I don't have to worry about it staying on all night.