I don't know that it's "natural", but when I've been having a hard time getting enough sleep, and/or I want to make sure I get to sleep and stay asleep because I have to get up early and that contrasts with my normal sleep schedule, what I take is doxylamine succinate (Unisom or equivalent store brand). I take only half a pill because if I take a full one I'll be groggy the entire next day. For me it takes at least an hour before it starts to kick in, and when it does it hits me hard so that I have no trouble getting to sleep. I find it to be very effective, and I get a very solid, restful sleep.
I have tried Sominex (diphenhydramine HCl, also used in a different version of Unisom) but found it to really have no effect on me. I've also tried melatonin and didn't feel any effect from it in terms of helping me get to sleep, but a friend of mine swears by it as very effective. Apparently, these things work for some people and not others, so you just have to try what's available and see what works best for you. Just be sure to never use more than the package instructions say to use. And it may be best to start with half the recommended dose to see how it affects you.