Many useful points here, but of course I have my own two cents' worth to offer.

You may find that drinking just before bed has a counter-productive effect in that the drink may help you drop off but the inevitable consequent need to pee will have you awake at zero dark thirty. For this reason, I generally avoid liquids after seven o'clock.

When stress is getting me down, the first indication I get is waking up at about four o'clock in the morning. I had several really stressful years during the 1990s, and at that time I learned to go to bed around nine o'clock -- when you go to bed at nine, arising at four just means you have time to do a couple of loads of laundry, read two newspapers and eat a decent breakfast before going to work. You can also let the cats out and get them in again before you have to leave the house.

The best way I found to send myself to sleep was to settle down with the lights off and the clock-radio on, set at "snooze" so it eventually turns itself off. CBC Radio I has a show called "Ideas" that begins after the nine o'clock news, and for years I would drop off to the gentle sounds of abstruse academic lecturing. To this day, words like "semiotics" and "discourse" induce slumber instantly. On the rare occasions when "Ideas" didn't do the sleep trick, I actually learned something.