My best advice this week is all in your mindset.
Be flexible- make list of the top 3-5 attractions you really want to see in each park. Then when you arrive focus on them and try to use the FP. Once you have done your top attractions the rest is just extra. Realize now that you will not be able to accomplish as many things that you have on other visits. But you will be visiting at an extra magical time. Xmas at WDW is incredible.
Midday Break- I preach this to all guest no matter when they visit. If you are staying at a Disney resort take advantage of the EE and then for lunch take a break. Leave the park hit a resort for lunch, go back to your hotel eat, nap or go for a swim. Then return to the park in the evening. The parks will be open very late that week so that is a definite advantage.
Crowds - at the MK alone it will be wall to wall people. Lines will get very lengthy, as in an hour or more. Like I said go with the flow and be flexible. Take time to just enjoy the surroundings. Dont stress yourself with a marathon thru the park where you have to do everything. This is the wrong approach to take during this busy week. Focus on the shows and displays that you would not normally see.
MK Tree lighting- everyday at 5pm a flag ceromony is held in Town Sq. It is so moving and they usually have a vet or current service person participate. Immediately following there is a cute show for the lighting of the tree.
CP- dont miss the best show on Disney property. If you arent in the holiday spirit after this one then you are definitely a Scrooge.
Resorts-Take time to visit the resorts. You have never seen decorations like this. GF is a good one, we go to tea, listen to the cms carol and then stay for the band who plays all the great holiday tunes. Not to mention the wonderful gingerbread displays. Even the FW guest decorate their campsites, they are incredible.
So stop worrying and think about all the new experiences you will be having. Have a magical time.