First you pick a time to sleep.

Say, you want to sleep around 9.

Then you do something relaxing and immediately go lie down after that activity when you want to sleep....

Your bed should ONLY be used to sleep and have sex. If you have a spouse it could be a good time to practice some quick love-making because that can help with satisfying sleep. Or some other self care. (Baths, showers, meditating, watching your favorite show, putting the kids to bed and then doing something relaxing, knitting, dishes? if that relaxes you...anything, really)

Try to do the same thing every night before you sleep and then try to lie down around the same time every night. (The sex thing you could probably do once a week. I have read that scheduled sex can actually be very fulfilling and that it doesn't need to be spontaneous all the time.)

At first, you will not feel tired when you lie down. You will probably lay awake for a few hours because you just don't feel tired! That is why you have to persist and continue with the schedule and TRY really hard to lay down by your designated sleep time. If you do it enough you will soon realize that your body will turn itself off. Your body will begin to associate 9:00 as sleep time and the activity you do before will help prompt this interaction.

When I was actually trying to keep a sleep schedule I would lay down around 11:00 pm and be asleep by 11:30 pm. Taking my pills at night prompted me into sleep. My body associates the action of taking medication with "lights out". I actually have a very hard time sleeping if I don't take my meds.

Another thing to note:

DURING WEEKENDS DO NOT OVERSLEEP/STAY UP. If you sleep at 9:00 every night during the week, do it during the weekend, too. You want to stay consistent with your sleep schedule so you don't confuse your body.