Contrary to popular belief, for people with insomnia, just lying down and not thinking of anything is among the worst things you can do. If you actively try to not think about anything, you become conscious of things you're normally not conscious of (for example, you'll start to actively breathe, and if you stop thinking about breathing if you end up in that situation, it's difficult to start passively breathing again unless you distract yourself), which causes you to stay awake longer, or causes you to seek out ways to distract yourself.
A good way for a person having trouble sleeping to finally get to sleep is actually to go through short stories. Just mentally act out the act of going and getting some food, or driving to the mall, maybe even imagine yourself shopping at the mall. Your brain will get distracted on that, and because you're not physically doing anything, you'll just go between imagining and dreaming and hardly know it until you wake up. It works wonders for me.