Since Epcot is so large, I always think that big crowds are handled well. For us, this was probably the easiest park to see between Christmas/New Year. If Mission Space is of interest, you should make a bee line for it and grab fastpasses (or jump right on if the line isn't too prohibitive). If Test Track is of interest, that should probably be your second priority. After you have the two most popular attractions out of the way, you can afford to slow down and enjoy the remaining attractions in Future World, picking up fastpasses as you go. I think the usual guidelines apply, but even more so when you're visiting WDW during the holidays. For me, those guidelines would be:
1) arrive early (having had breakfast before you get there)
2) pick up the park map AND the show schedule
3) know which attractions you plan to visit and the order of the first few (or all of them if you're a manic planner

) - like goofy4tink we have "must sees" and "would be nices"
4) know which attractions have fast passes and work around that
5) make a PS in advance if you plan to enjoy a sit-down meal.
I'm not sure if you've been to Epcot before, but on a typical day when it's open from 9 - 9, and assuming I was devoting 1 day to the park, I would probably budget my time roughly as follows:
9:00 - 2:30 - Future World (grabbing a counter service lunch)
2:30 - 7:00 - World Showcase
7:00 - PS in one of the World Showcase Restaurants
9:00 - Illuminations
The Candlelight Processional runs until December 30th, and there are also special Holiday storytellers, etc. at the countries in World Showcase, in addition all of Epcot's usual attractions.
Here's the link to the current schedules for each park. You can click on "Epcot" at the top, and then scroll down a bit and click on "Holidays Around the World: November 26 - December 30" to get information about storytelling & other events.
If there are children in your party (say 5 & up) you might want to consider either buying a World Showcase "passport" which the children can have stamped in each country and/or making a mask with add-ons from each country. Both of these things are done at the Kidcot centres in each WS country, but sometimes the lines are prohibitive.
Hope this gives you some ideas!