There's nothing like Disney at the holidays! I go every year or two and take it all in. So let me give you some of my best tips:
Definitely hit Epcot at night. There's nothing like seeing the tree (although that's true of most of the parks, and many of the resorts!), hearing the candlelight processional, and looking at the decorations from each of the different countries.
Unfortunately, there wont' be an Osborne lights festival this year. That's always one of the most amazing aspects of Xmas at The World.
Hit the resorts if you have the time! The Wilderness Lodge is my personal favorite, althought the Grand Floridian also does a beautiful job (and although you probably won't notice the difference if this is your first holiday trip, as amazing as the tree in the GF lobby looks now, it's usually much, much bigger, as has been the topic of much heated discussion on the boards!)
Definitely do Mickey's Very Merry Xmas Party one night. Find out when it is, and get tickets. Especially if you're going at a time when the Party will be offered midweek, which is always less crowded than those on the weekends. Of course, the closer it gets to Xmas, the more crowded everything is, period!) When else will you get a chance to see it snow on Main Street?
Make sure to see the holiday parades when offered.
This year, the Wilderness Lodge is offering 30 minutes sleigh rides through the woods around Fort Wilderness. They need to be booked in advance, and cost $30.
Those are my top hits!
Richard