We were there Dec 27-Jan 2....while it was definitely busy, we planned well and had a blast. My suggestions....
--READ, READ, READ the DIS as much as possible...you have plenty of time!
--Get there early! We utilized the morning EMH and walked into each park at 7am that week. We were able to do so much those first couple of hours with no waits! We enjoyed the park, met characters, used our fastpasses, ate lunch and left for a nap.
--Collect fastpasses. Remember that you can use them even after the time frame listed on the ticket. On the busiest days, collect them early because they can run out of fastpasses for the day. (If you are leaving and trying to come back in the evening, collect as many as you can before you leave)
--Make ADR's as far in advance as possible. Keep trying if you can't get what you want. We had to change one while we were there...and I was able to get something I wanted for Jan. 1st and I was calling the day before.
--If you have a young child, utilize the child swap system. My 6 year old was able to ride everything twice...he was thrilled! Just ask the cast member at the entrance to the ride to get the pass.
--We went to AK on NYE....by far the least crowded park that day. It was very pleasant.
--We have young children, so we did not stay out late on NYE....we went to MK at 7am New Year's Day and felt like we had the place to ourselves! We were the only ones on the teacups...we walked right onto every ride in Fantasyland (and even did several twice in a row). We walked right onto Buzz Lightyear, met the princesses right at 9am with NO wait. We even came back that night and it wasn't too bad of a crowd.
All of this because of what I learned on the DIS! I was a long time lurker and am glad to share what worked for us!