Talk to the experts at a major hospital closest to you. Most countries can recommend a sleep research facility who can identify the causal factors of your problem.
Possible causes are sleep apnoea and medically related conditions
Otherwise Basic rules are,
No caffine, this includes most soft drinks check the ingreedients and you could be surprised
No heavy meals within a few hours of "normal" bedtime but a good diet is essential
No alcohol for a while as it affects REM sleep
Stress is a major contributor to insomnia so clarify and identify stress sources. Seek advice if necessary. Conditions such as Post Traumatic Syndrome require the experts as symptoms from insomnia to suicidal tendencies can manifest themselves years down the track. The condition can arise from many different events such as a vehicle accident, loss of a loved one, a marriage breakdown or loss of employment.
Reform the bodies sleep habits by going to bed at a normal time and then reading your regulations each night. I can never make it past page five on a bad night. David Attenbouroughs video "The Secret Lives of Plants" is a good nightcap.... zzzzzz zzzzzzz zzzzz
Exercise and physically encourage your body to work then rest. The rest time is critical and dont exercise a few hours prior to sleeping as the body is still in the "wound up" part of the cycle. Your heart rate should be elevated for about 20 minutes continously each exercise period. Check with the doc as to what exercise regime is best for you.
Are you "napping" during the day? this doesnt usually help most times but in cirtain cases is used to suppliment the normal sleeping patterns of an individual under stressful conditions
Your environment could also be a contributing factor, from sudden sporadic noises outside, to a bad matress. Flashing lights reflected in a room also keep the body "on alert"