1) It's preferable that you have regular sleeping cycle, meaning you sleep at the same time of the day. That way your body adjusts to "sleep mode" faster.
2) Abstain from stimulants such as caffeine or nicotine.
3) Despite what others say, I cannot agree when it comes to video games. As video games are exciting and addictive, I end up staying late at night. I can say the same with watching TV or books (or any other stimulating activity), unless you happen to find those activities boring.
4) If you are hungry, a light meal is okay. Overrating may stress your digestive tract and disturb your sleep.
5) Alcohol can make you drowsy and put you to sleep, but it's not quality sleep...and can develop dependence.
6) Take a warm bath/shower.
7) Learn
relaxation techniques: the goal is to relieve physical tension and distracting thoughts that are stressing you out, which may be cause of lack of sleep.