Depends a bit on the reason but here's a couple of general tips - No one thing necessarily but a number of good habits together will help. Here's a mix of things to try.
Exercising approx 4-5 hrs before going to bed will coincide with a slight drop in body temp at your bedtime which makes falling asleep easier. (Even a good brisk walk a few hours before bed should help).Helps reduce stress too.
Avoid caffeine in any form in the few hours before bed.
Not sure if this relates to your situation - but your bedroom should be a place for sleeping so don't use your bedroom as an office or to do work in.(you want it to only be associated as a place for rest (some exceptions :-)
You sound like you may be a little stressed(diff relaxing) -if you tend to worry a lot and think when you go to bed a good strategy is to write down the things you think you need to be worrying or thinking about - allows your mind to let go a bit "i won't forget those thing now i can deal with them tommorrow"
Don't spend your last hour before bed on the computer etc - can leave the mind too active to drift off.
There are meditation cd's and music etc that are good for helping the mind relax before bed - something you could make part of your daily bedtime routine.
When you do lie down - try not to focus to much on trying to fall asleep - try to just be happy you're relaxing. Sometimes even telling your self you're not going to try to fall asleep can actually help even though it sound a bit counter-intuitive.
There are natural/herbal remedies and tablets you can take to help - i know some people who swear by them. The act of just taking something can help too sometimes.
Obviously you could go to your doctor for a short-term supply of seeping tablets - but that should be a last resort.
Funny picture btw. GL hope it gets easier - can be quite frustrating when you have difficulty falling asleep.