Jesus christ I just typed out a massive reply then the internet went down. Great.
Anyway. As Jamie says, try and going to bed earlier - around 11pm is good (if you are aiming to wake up at 7am). If find if I go to bed at 11 I will get to sleep quickly, but if I stay up working or whatever till 1am etc I won't be able to get to sleep for another couple of hours.
As others have said, try not to do anything too engaging before going to bed. Reading helps, but playing games etc does not.
You could also try muscle relaxation techniques. Contract your muscle groups for 20-30 seconds and then relax them again, start from the feet and work up to the upper body. This can help before sleep.
Alcohol and caffeine are both disruptive to sleep patterns and so shouldn't really be drank before going to bed, although beer may help initially, it shouldn't really be recommended, especially not in the long term!
Or, as Dan says, just bosh one out. That usually works as a cure for most things, including hangovers as it happens