I frequently enjoy a snifter of beer before retiring of an evening too, but too much liquid before going to bed can sometimes be a bad idea!

(it can also prove slightly addictive

)
I've found that certain activities during the evening can increase the chances of having trouble getting to bed, like looking at a screen all evening, be it TV, a computer monitor, or even a mobile phone screen (damn that Monopoly game!) Also, too much excitement (like playing a computer game) is sometimes a bad idea too.
You also need to optimise your environment... make sure your bed is comfortable and that it's ready (i.e. made!!) for when you want to use it. Extinguish as much extraneous light and sound as you can, a simple pair of foam earplugs can help with that, and thicker curtains and shielding lights from alarm clocks/hi-fi's etc. can help create a perfectly dark environment.
Total silence might not be possible or even desirable, however... some quiet music is good, especially familiar and/or relaxing music... I don't mean rush out and buy 'Pan Pipes Of The Andys' (Famine's favourite CD, so I hear), just something you know very well and enjoy. Unfamiliar music or chat (like on the radio) can be distracting...
Failing all the other helpful suggestions, you might want to try something a bit more bizarre - which, oddly enough, I sometimes used to do when I was really struggling to get to sleep, which was chanting a mantra inside my head... Believe it or not, I used to chant the
Hare Krishna maha-mantra inside my head (for goodness sake don't do it out loud, you're Mum will think you've gone nuts

) and even after a few minutes I was finding it difficult to keep track of which half of the mantra I had just read. You quickly become sleepy and end up giving up and hopefully falling asleep shortly afterwards...