Have patience!!!
The parks are going to be at their busiest. As I would recomend at anytime, ride the usually busy rides at the times the parades are going on. Last time I was there for new years, Haunted Mansion and Country Bears were walk ons because every one was out watching the parades, and yes this was on New Years eve.
And if you're staying till midnight, have patience leaving too. It took me over 45 minutes to get from the hub to the train station.
-Sulley