I'm not going to be much help in this area. I'm so used to only getting a couple hours I wake up a bunch of times throughout the night if I go to bed at a decent time. When I really want to get a good nights sleep I take a couple of Tylenol PMs. I have thought of trying Melatonin but feel weird about taking something every night.
What about eliminating caffiene, trying either white noise or a soothing sounds CD, meditation, or a relaxing bath? Chamomile tea is supposed to be very relaxing as well.
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"I never understood why blessings wore disguises. If I were a blessing, I'd run around naked." - Sophia Petrillo
Avoid alcohol or cut back. Red wine especially makes me sleepy but after a few hours, I am wide awake.
(and to add to Aardie's..white noise can be as simple as tuning to am on the radio and putting it between stations so all you get is the static noise...and turn it down, of course)
Agree with white noise and lowering the temperature. I need both to fall asleep/sleep well.
My dad also taught me a trick when I was young to help me fall asleep quickly (though it probably won't keep you asleep). Find a comfortable sleeping position and concentrate really hard on completely relaxing one body part at a time starting at your toes and moving up. It's amazing how tense you can be without realizing it, plus it helps takes your concentration away from any worries or busy thoughts. I rarely got past my knees when doing this.
I don't have much useful advice for staying asleep or sleeping for longer periods. As others have said, avoiding caffeine and alcohol might help, as might avoiding drinking too many fluids of any kind before bed if you're waking up because of your bladder (this happens to me a couple times a night, but I'm good at getting back to sleep).