Circadian rhythms direct a wide variety of functions from daily fluctuations in wakefulness to body temperature, metabolism, and the release of hormones. They control your timing of sleep and cause you to be sleepy at night and your tendency to wake in the morning without an alarm. Your body’s biological clock, which is based on a roughly 24-hour day, controls most circadian rhythms. Circadian rhythms synchronize with environmental cues (light, temperature) about the actual time of day, but they continue even in the absence of cues.
The latter portion of this plan is meant to tidy up some of the loose ends, including conditions that can undermine sleep. If the early changes haven't proven to be effective or relevant, it may be because other issues are at play. Ultimately, if your efforts aren't rewarded in the end, it may be useful to speak with a sleep doctor who can provide you the personal assistance you need to overcome any remaining problems. This advice is generally good for all, but carefully crafting it to attend to your individual needs may make it invaluable.
Give yourself some dedicated wind-down time. It doesn’t have to be a full hour or an elaborate routine, but try to spend at least 20 to 30 minutes doing something that relaxes you before you try to fall asleep. That could be taking a warm bath or shower, changing into comfy pajamas and sipping a cup of chamomile tea. Or something completely different — so long as it’s relaxing to you.