Obtaining adequate, regular, high quality sleep is perhaps the single most important thing you can do to improve and maintain your health. Based on hours of research and personal experimentation, below are the things that I find most effective in improving the most important aspects of sleep. Specifically - time to fall asleep, sleep duration and overall sleep quality.
Wear glasses that block blue light for at least 2 hours before bed. Blue light suppresses the production of melatonin by the pineal gland. Melatonin is extremely important in maintaining your circadian rhythm. People without adequate melatonin production typically have problems falling and staying asleep. Low melatonin has also been linked to other health conditions such as cancer and diabetes. It's also a good idea to replace the light bulbs in your bathroom with amber bulbs that emit little to no blue light. If you find that blue blocking glasses become less effective over time, try taking 500 mg of tryptophan on an empty stomach before bedtime a few nights a week.
Only eat during daylight hours. It's believed that food can influence the circadian rhythm as much as and perhaps even more than light.
Sleep in a completely darkened room by using blackout shades or blinds. If this is not an option, the next best thing is to wear a night mask.
Sleep on your side. People with sleep apnea tend to sleep much better on their side than on their back or stomach. Studies have shown that this also applies to people without sleep apnea.
Avoid alcohol within two hours before bed. Alcohol can help you fall asleep but it can also dramatically reduce REM sleep, which is the sleep phase where memories are stored and consolidated. Alcohol before bed is also more likely to cause you to wake up too early, often in the middle of the night.
Get light exposure early in the morning, preferably from a short 15 - 30 minute walk outdoors. If you live in an area where early light exposure is impractical, an artificial light box also works. A product that I use occasionally for this is the Philips goLITE.
Watch ASMR videos for 30 minutes before bed. While controversial, strange, and creepy at times, ASMR can be remarkably effective for inducing relaxation and sleep. Unfortunately, it doesn't work for everyone. For best results, watch the videos in full screen and use earphones.
Consume 2 - 3 tsp of raw honey immediately before bed. Honey is believed to have a stabilizing effect on blood sugar for approximately 6 hours. When blood sugar drops too low, the body releases stress hormones to raise it back up. This is one of the main reasons why some individuals wake up frequently during the night / experience periods of restlessness.
Experiment with binaural beats that are designed to induce delta brain waves, which can improve deep sleep.
Monitor your sleep using smartphone apps. Apps like Sleep Cycle and Smart Alarm monitor movement and sound during the night to calculate an approximation of sleep quality. This can help you determine how certain behaviors and even different foods impact your sleep. Additionally, many of these apps will wake you up softly during a light sleep phase, which helps ensure you wake up feeling refreshed rather than tired and groggy. Of the two apps mentioned above, I prefer Sleep Cycle as it seems to be much more sensitive, whereas Smart Alarm tends to give me roughly the same score (+/- 1%) every night.