There are so many. Potential causes and aggravating factors, the first thing to do is see a sleep disorder specialist after you see your family doctor.
Sleep hygiene is key. Retire & rise same time each day. Bedroom should be dark & cool - used only for sex & sleep. Turn off tv. No naps. Exercise regularly but not in late evening. No caffeine for 6 hrs & no alcohol or tobacco w/i 2 hrs of sleep. Dinner should be moderate sized & finished at least 2 to 3 hours before sleep. Can try warm milk, chamomile tea or melatonin along w light reading, warm bath, lavender scent.