I'd say look into good sleep hygiene first -> having a regular routine, avoid caffeine after noon, only use your bed for sleep and sex, don't drink close to bed time, breathing/focus techniques, etc. There are some good reads on it if you google around.
For otc meds, I have had some success with melatonin and valerian root (independently). I'm trying valerian root + hops tonight. Some people seem to have success with Kava and Taurine. Just be sure to do your homework for anything recommended by anyone including your Dr.
Good luck!