I've found a pretty effective means for me to fall asleep when I have insomnia characterized by racing thoughts: I simply count from one to four over and over again, non-stop until I fall asleep.
Now some details, background, and theory regarding this method. The idea behind it is to try to keep the mind occupied so that it doesn't have a chance to think about all those things that keep me awake.
In the past I'd tried a bunch of different methods for falling asleep, including the common one of counting from one to a hundred (or backwards from one hundred to one), but found that I would often lose track of where I was in the count, and have to start over. This minor annoyance was why I decided to count a much smaller number, so I'd never lose track of where I was.
Another problem that I had was that if I counted too slow, then some thought would sort of "sneak in" in between the numbers and there'd be some chance that I'd start thinking about that rather than continue the count. To counteract this I started counting faster, and found if my counting was fast enough and if I tried to focus on the count rather than letting my mind drift while counting automatically, it usually worked pretty well at letting me fall asleep.
Now, this isn't foolproof, as major anxiety, the effects of stimulants like caffeine, physical issues such as pain, etc, can overwhelm such a method, but for more "ordinary" insomnia caused by racing thoughts I found this simple method to be quite effective.
Incidentally, chamomile tea will make me drowsy, and so will small doses of melatonin, and if I don't fight the drowsiness and try to fall asleep as soon as I get drowsy, that often helps too.
Something else that helps is being slightly chilly. Not so much that the cold keeps you awake, but just enough for that the blankets feel comfortably warm. Being either too hot or too cold is bad for sleep.
Wearing earplugs and a blindfold can help, as can pot, if you get the right strain and the right dose.
Finally, I've found that certain types of food (like a big bowl of pasta) will make me pass out, even at inconvenient times like that middle of the day. I haven't tried eating as an insomnia cure, since I generally don't like to eat big meals before bed time, since digestion stops for me while I'm asleep and waking up with a half-digested meal can sometimes be uncomfortable.