Make sure the office is talking about you for the RIGHT reasons the next day...
Do give yourself enough time to plan the party properly - booking a venue in summer is the best idea.
Do stick to your budget. This is not your money and your boss will not be impressed if you go over your allocated budget.
Do ask around before booking anything. You might think that having a curry for your Christmas party might make a welcome change to tradition but everyone else might be looking forward to some turkey.
Don't sit on the photocopier.... It's been done to death and it's not pretty...
Don't get too drunk! It seems a good idea at the time but don't forget that these people are your employers and work colleagues and you will have to face them again sober on Monday!