Michelle, You didn't give us a lot of time, and while you are right that a whole lot of information resides here...we can be very conflicted,opinionated and contradictory, so ultimately you will have to make final judgements.
I would suggest you stop off at Barnes and Noble (or other favorite bookstore) and pick up the Unofficial Guide to WDW. Also check out another site:
www.allearsnet.com for some good suggestions and ESPECIALLY for the listing of menu's to help you plan meals, particularly if you like nicer, sit down dining.
One important question that was already asked is if you are staying on property. If you are, it makes a lot of things easier including transportation and as was mentioned, each day you have 1 hour earlier entrance to a designated park. Two other preparations, either on the web or when you get to your hotel, get park maps and familiarize yourself with general layout. Also with park maps, get a listing of shows and events. When you know when the parades are or fireworks, you can plan around them. Then understand fastpass as it will help you see the most (as far as thrill rides). Finally, never feel shy in asking a Cast Member, any Cast Member for help. They enjoy the interaction and can usually help in an uncertain or confusing situation.
OK, on to the parks:
Magic Kingdom: Off to your left after Main Street, you will find Splash Mountain and Thunder Mountain. Splash usually gets a longer wait time, so FastPass (FP) that and go on Thunder. Behind the Castle is Fantasyland that you may want to walk through but not linger with limited time. Tomorrowland (right at the end of Main Street) is home to Space Mountain that you would enjoy. There are many other rides and events for you to experience as time permits. Do plan on seeing the fireworks show, Wishes, it's a must.
Epcot: Go to your left past SpaceShip Earth (big ball) to Test Track then Mission Space (may want to FP Test Track). If the Wonders of Life pavilion is open do see it as it may not be long for this world. Then you can see Energy, cut across the plaza to The Land, Imagination, then later to Spaceship Earth when it's not crowded. The countries around the lake are my favorite part of Epcot, but with limited time, you judge as to how much time you want to spend there. It is a slower paced kind of enjoyment. In the evening the fireworks show Illuminations should be on your agenda.
Animal Kingdom: At park opening either go to Dinosaur or the Safari. These are the two highest volume rides. you will also like It's Tough to Be a Bug (inside the Tree of Life) and the Legend of the Lion King stage show which should not be missed. You can get a good look at AK by early afternoon and park hop back to MK or Epcot if you want.
MGM: The two "thrill rides", Rock 'N Roller Coaster and Tower of Terror are to the right after a wall down the main street. Fast pass one and ride the other...repeat as desired. You would probably also want to do the Great Movie Ride, Star Tours and the Indiana Jones stage show. You may want to include Fantasmic in the evening.
Of course there is so much more that you will discover on future visits, and I did not discuss dining. If you hit the "big" rides first thing, you should still have time to kick back and just enjoy the parks without running yourself ragged. The Christmas crowds should be tapering off, so you should not have too much crowding in the parks and may have easy access to all.
Enjoy!
