Don't "over plan". Leave at least one day wide open, then take a vote and do what everyone most wants. It may very well be the most fun day of your trip.
Don't be park commandos! Savor the moments. You'll never do it all in one trip, so don't try.
Plan your days well, but be flexible - things change.
Don't feel that taking a break or a nap is a waste of valuable vacation time. Nobody can enjoy themselves if they're burned out. RELAX!
Use some unique colored ribbons and tie some onto your luggage. All luggage looks the same when it's going around on the carousel at the airport, but when mine comes around with obnoxious lime-green ribbons all over it, there's no mistaking it!
Tip the Mousekeepers. They work hard for peanuts and they appreciate the tips. The level of service and attention goes up when you do!
If you have young kids, get them "Guest of Honor" badges before you go. CM's will call them by their first names all the time, and it really makes the kids feel special.
Take a video camera, just don't have it attached to your face the whole trip! These tapes provide priceless memories. Just think of how much fun they'll be to watch in 20 years...
Final Tip: Never ask DIS'ers to give only ONE tip! We have too much to say
'Beano'