It should not be too cold, too hot, brightly lit, or noisy. Don't drink liquids or eat more than a light snack before going to bed. If you suffer from heart burn, avoid food for several hours before bedtime. If you can't go to sleep in 30 minutes, get up and get involved in some relaxing activity such as reading or listening to soothing music until you feel sleepy. Avoid caffeine and alcohol.
Caffeine can delay sleep.
Alcohol may interrupt sleep late in the night. Don't take long naps. Fitness can improve sleep, particularly as we get older. Also, an evening walk seems to help most people relax and fall asleep more easily.