I am currently reading Why We Sleep for the 3rd time. Fascinating reading, highly recommend it!
Melatonin only works on the timing of when you fall asleep. It can not generate sleep. It's a bit more effective for dealing with jetlag.
He says limiting caffeine 9 hours! before bedtime, as it has a half life of 5 - 7 hours.
Lots of really good info in the book about sleep and all things that affect it.