First, I am a loyal subscriber to TouringPlans.com, which unlike Tour Guide Mike, can pretty accurately predict the best park of the day about a year in advance.

That helps me to map out a basic itinerary.
Second, I look at the historic park hours listed on WDWinfo.com,
http://www.wdwinfo.com/wdwinfo/hours.htm which helps me to figure out what I want to do as far as hopping versus not hopping through my trip to maximize the fireworks, parades, and such.
Third, I go on a "fantasy vacation" in my head. Along the way, I take into account what we want out of our vacation. I know what we like to eat. I know around what time that I want to eat at the parks based on things like, did we do rope drop or did we sleep in, are we going to be on "thrill rides" early or later in the day, and so on. For menus around WDW, check out allears.net.
http://allears.net/menu/menus.htm
Basically, it's a juggling act. For our upcoming trip we have two
MVMCP's and one day for each park. We won't be doing any hopping. We have planned for the following ADR's based on the needs laid out by our plans.
We arrive late on the 8th. We have no plans that night other than settling into our CL room at the YC resort.
Kouzzina by Cat Cora at Disney's BoardWalk Resort
Day & Date: Sunday, December 6, 2009
Breakfast
MCMCP
Day & Date: Sunday, December 6, 2009
Les Chefs de France at Epcot
Day & Date: Monday, December 7, 2009
Lunch - will cancel if Remy has left for HK
Tutto Italia Ristorante at Epcot
Day & Date: Monday, December 7, 2009
Dinner - may cancel if we do have lunch with Remy
Kona Café at Disney's Polynesian Resort
Day & Date: Tuesday, December 8, 2009
Breakfast
MCMCP
Day & Date: Sunday, December 8, 2009
Wishes Dessert Party at Magic Kingdom Park
Day & Date: Friday, December 08, 2009
The Plaza Restaurant at Magic Kingdom Park
Day & Date: Wednesday, December 9, 2009
Lunch
Disney's Grand Floridian Resort & Spa - Garden View Lounge
Day & Date: Wednesday, December 09, 2009
Afternoon Tea
Wildlife Discovery Excursion at Disney's Animal Kingdom
Day & Date: Thursday, December 10, 2009
Morning Excursion
Yachtsman Steakhouse at Disney's Yacht Club Resort
Day & Date: Thursday, December 10, 2009
Dinner - "date night"
Mama Melrose's Ristorante Italiano at Disney's Hollywood Studios
Day & Date: Friday, December 11, 2009
Dinner
A few things were added along the way, but our plans were pretty much set months ago, like two MVMCP's instead of just one, but I get to meet a DIS friend because of it.

We caught a deal on a CL room, so we added in the Wildlife Discovery Excusion, which we are very much looking forward to doing. The Wishes Dessert Party was added because it just fit into our plans on that second MVMCP night better than it would have during the one when we meet my DIS friend. We added a dinner at the Yachtsman because we decided that we wanted a "date night" at WDW and since we are staying at the YC, this will be super simple to work into our plans. We had to switch out a few of our park days because of the Pop Warner events, which made booking a dinner at DHS a nightmare. We added the lunch at Les Chefs de France, only because I so wished that I could have shared seeing Remy with my partner when I went to WDW solo earlier this year. Knowing that Remy's departure has been delayed and that there are CM's on another board posting that there is a casting call out for more people to be presenters for Remy at Chefs through the end of the year, well, that was enough to make me book a reservation even though he might still leave.
In the end, we got everything that we wanted.

I can't wait!

Maggie