Many workplaces celebrate the holidays with staff parties.  These parties can be joyous events or career landmines.

• Dress appropriately.  You don't want to look too casual or too flashy.  If people remember what you wore, you've probably overdone it.
• Don't overindulge in any way. Your fellow guests are people who rely on you in a professional way.  You need to always communicate reliability and responsibility.  Getting drunk and telling off-color stories doesnot communicate a helpful message.
• Do use these parties to get to know people you don't typically work with.  You can learn more about the organization, build relationships for future projects, and maybe even make a new friend.
• If you bring a guest to the party, don't abandon him or her until you've introduced at least a few people. 
• Make it a point to thank those reponsible for organizing the party.  It's a lot of work and thank yous are always nice.