In reply to Liam Copley:
Most important is good insulation from the ground, you need a good thick full length mat. I take a thermarest and a karrimat and use both if weight is not an issue.
A warm sleeping bag is also good. You can improve your sleeping bag with a liner and you can always wear socks and hats and thermals if you need to. If possible keep a dry set to sleep in.
Make sure you have got some where you can get water from if outdoor tap freezes.
Make sure you have got LOTS of warm clothes. Keep warm during the day so you don't feel cold going to bed.
Take a small tent rather than a big one if you can, it will be warmer.
If you can camp somewhere where you are allowed a fire that would be pleasant.
Don't drink lots of alcohol, it takes the heat away from your core to your skin and can be a factor in hypothermia (not to mention that if you are too p***ed you might forget to get into your sleeping bag.
If you have a platypus or sigg bottle you can put warm water in it as a hot water bottle. Be careful not to burn yourself.
Make sure you have a hot meal in the evening it warms you from inside. Hot drinks are good too even if you don't normally drink them.
Have a good time