I know of two things that help. One is exercise, which lots of people have mentioned here. The other is meditation. My brother-in-law suffered badly from insomnia for years and says it made the biggest difference out of all the things he tried.
I have chronic insomnia. Now that I'm walking home from work (about 35 blocks), I feel even better, and my insomnia is worse. I tried resetting my circadian rhythm by not eating 16 hours before going to bed: even worse insomnia. Anything I do to control my insomnia exacerbates it.
That sounds hard, and I'm sorry to hear it. If your point is that your experience contradicts my statement, I agree. Had I run the "comment" command with the -v option, it might have taken the following more accurate form: "I know of two things that have helped me sleep better, although I didn't have insomnia to begin with; somebody else I know who does, reports that both helped him too, but of course it doesn't mean they'll help you, but they might be worth trying."