Autogenics is a biofeedback technique that induces a state of intense relaxation. It's supposed to be able to help change compulsive behaviors, though I haven't tried that myself. I have found it very helpful for getting to sleep, though, and pleasant as well. I used this guide for what I have done so far.
Fun anecdote: Once, while I was cuddling with my boyfriend, he said, "I can hear your heartbeat!" A few moments later he jerked and looked at me in shock. "It just slowed down!" :-) I felt like a wizard. Biofeedback is cool.
It's probably worth trying if you have problems sleeping. Interestingly, it's found to be useful in treating a several mild mental and physical problems, like headaches, anxiety, mild depression, and sleep disorders. It's also used for pain relief for natural childbirth. (Meaning, for women who don't want to have an epidural.)
The recommended practice time is quite long, is that to be able to do it at will or something? See for example this Youtube video which was effective for me today, and this is the first time I've tried this.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.