No stressors in the room where you sleep. If there are outside lights that go on and off, get a blackout curtain for your bedroom, just for sleeping, though I like to be awakened by morning light. If you are young and growing and tolerate milk, then a snack of 6 oz of low fat milk and 1/2 of a meat sandwich on whole grain bread, 2 hours before bed time can help, but not close to sleep time. If there are distracting noises in the house then get one of those little fake waterfalls, and run it while you sleep, and train your self to focus on that sound, rather than others.
Teenagers stay awake well past midnight, and want to sleep until noon. This is without fail. Now, researchers say that the end of puberty is marked by a return to a more heliocentric sleep cycle. High Schools across the nation are setting back their intimes to accommodate the sleep needs of adolescents.
There is this work ethic afoot that says making them get out of bed is good discipline, and that is rubbish. Their natural state would be slow in the morning, but energetic late into the night, perfect for harvest activities, and their social lives.
Insomnia for the teenager, early evening insomnia, is the natural state.