DW and I went from 12/22-12/27 of this year. Before Dec 25 the crowds were manageable. Get as much done before 12/25 as possible. I recommend doing MK and MGM before Christmas as they tend to be the most crowded after Christmas (Epcot is bigger and not as kid friendly and AK still doesn't have as many people wanting to see it as the other parks).
Get to parks early, use Fastpass as much as possible, and take advantage of the later hours. Don't be afraid to leave for a few hours in the middle of the day and nap. After dinner the crowds tend to thin out a little bit.
Have a plan of action for which rides are most important to you and when to try to do them. Do the major rides first. Test Track had 2-3 hour waits by lunch and all FPs had been distibuted by then. You may have to criss-cross the park a few times in the AM but you'll be glad by noon that you've gotten the major rides out of the way without too long a wait. All that being said, be FLEXIBLE and understand that your plans are not rigid and will have to change depending on what else is happening.
Make PS for all sit down meals. Book any shows (Cirque, Luau, Hoop-de-Doo) early.
If you realize you can't do/see everything and just enjoy the atmosphere you should have a wonderful time.