Stimulants are a big no-no. The most common are caffeine, alcohol and nicotine. It's best to avoid these in excess especially caffeine late in the day!
A routine with your sleeping schedule is helpful for a good nights rest. Wind down at a certain time nightly and stick to a regular bedtime schedule. In your brain there is a gland that puts out a hormone that helps with sleep/wake cycle (Melatonin). When you establish a regular sleeping pattern, Melatonin will adjust to help you to have a restful sleep at that time.
Exercise early in the day. The stress hormone, cortisol, will keep you awake at night if you exercise too late. You should exercise no later than 2 hours before your expected bedtime to have a restful sleep.
No computers, or t.v. in your room. If they are in there, unplug when you are not using them. They put off electronic energy that will disturb your sleep.
Sleep in a dark room! Melatonin has a nocturnal cycle that will be disturbed if a light in the room is on at night. If you go to the bathroom at night - just leave the light off. Turning it on will disrupt this nocturnal production and cause the diurnal cycle to start - waking you up enough that you will have a very hard time getting a restful sleep.
Serotonin levels matter! If your Melatonin cycle is out of balance you need to work on getting your Serotonin levels up. I test neurotransmitters here in my practice and I'll bet over 85% of people first tested have very low Serotonin levels. Your body makes Melatonin out of Serotonin. I am not talking SSRIs (prescribed anti-depressants). Those do not raise your levels - just recycle what you currently have. I am talking about B6, tryptophan, L-theanine, and Inositol to raise and balance Serotonin levels. This also helps with depression and anxiety, and of course, insomnia.