If its because of stress, resolve mental or emotional problems. If its because of uncomfortable-ness, try a hot drink or bath before bed. If its because you just can't seem to shut down or slow your body down to go to sleep, take a 1-5 mg melatonin (it's a natural med that is even safe for kids to take that makes your body sleepy, no weird side affects)
there is a sleeping pill you can take before sleep or even in the middle of the night if you wake up and can not get back to sleep. it is sold over the counter too. sorry i just cannot think of its name ,you can ask the pharmacists though . also, walking during the day at least a mile will help you sleep at night. try getting one of those noise machines with the sound of waterfalls,rain ,birds, ect,,(sharper image carries them) try using lavender sense on your pillow case. take a hot bath before bed.