What helps me the most is the temperature of the room, and it must be cave-like dark! I love to have the room slightly cool (which is difficult in Texas summer!!), and to curl up with a blanket.
According to Division of Sleep Medicine at Harvard, the ideal sleeping temp. ranges from 60-75 F degrees.
Should you nap or not? If you are having trouble sleeping at night, and nap during the day...try to take naps before 5pm and keep them short...that might help you sleep better overall!
Best tip, and one that is most difficult: keep same bedtime and wake-up time, even on the weekends! Consistent sleep schedule is crucial to setting your "internal clock".