some info to gather off the sites that vald1977 suggested or a guide book (if you get one - my fav is the mini mickey. nice and pocket sized):
best days for which park for the time of year you are going
interesting places you may want to eat during your trip. (some of these you may have to make Priority Seating ressies for. - depending on when you go the hottest eating/dinner shows book up early.)
have the kids and hubby (or whoever is going) get involved. check out decriptions for each attraction at each park. have each person list their "must sees" and "no thanks" attractions. If this is your first trip you may have to skip a few things for the sake of time. This way you can get to at least a few of everyones "must see"s.
And this sounds funny coming from me (considering what i just said above).....don't go to nuts with the planning. Factor in some time to relax and enjoy the surroundings. Don't force you family to rise at dawn and bust the parks wide open if they are not morning people. (that is the best way to beat the heat and get the most done out of your day, but if you group is not a morning one, you will just annoy everyone and ruin the vacation for all of you.)
Don't be afraid to split up if some of you have different likes/dislikes. We have met the late sleepers in our group at a certain spot at a certain time. (we already had a few hours of park time in - feeling good about what we had accomplished. They felt more relaxed and refreshed as they had just slept until 10:30.)
- good luck, happy planning, and have a great vacation.
Get yourself a good guidebook (or two or three 
). I really like the Unofficial Guide as well as Birnbaum's Official guide. There are also others out there geared toward traveling with different age groups.
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