There's people who've been going to WDW for years, and even many of them haven't done it all. There's just so much to see and do there, you'll never get bored.
But lets say you just stick with the 4 theme parks and not do the water parks on your first trip. Like Tinkermell said, I would schedule 2 days for MK, 2 days for Epcot, 1 day for AK, and 1 day for DHS (used to be MGM).
The shows can take up a large bulk of your time, so if you just pick one or two shows you really want to see at each park, you'll be less rushed and able to relax and enjoy the parks a bit more. Just go in knowing you won't be able to see and do it all during your first trip. Pick the things you really want to do on your first trip and stick to that plan.
As a first time visitor, I also think it's important for you to stay on property. It's just so much easier to stay on property and take advantage of Magical Express, as well as the bus/monorail/boat transportation. There's no getting lost.....no asking for directions.....no car rentals.....no worries. You can just relax and enjoy!
We also used the dining plan when we were there and found it very convenient and a good deal. It's not as great a deal this year, but for some, it's still a better deal than paying menu prices.
Also, we're never up early enough to do the morning EMH (yep, we're on vacation, so we sleep in!), but we LOVED the evening EMHs and got a lot done in just a couple of hours. However, we went during low season, so the evening EMHs weren't very crowded at all.
The travel time of flying across the country is a bummer though. Basically a whole day waisted flying to Orlando, and then another day spent flying back home. UUHHHHHG!

This one thing can make me have second thoughts about going to WDW because DL is only a 2.5 hour flight away. As a matter of fact, I
think we're going to WDW this year for our family vacation, and I'm in the beginning planning stages, but I keep having those second thoughts I was talking about. Especially these days because DLR is just getting better and better!
If only they'd build an Epcot at DLR (or something just as great).....I'd probably never go to Orlando.
But, with the four great parks at WDW, and the huge variety of experiences offered between them (as well as the resorts and restaurants), it really does make those long travel days worth it. And I'll admit, we ended up loving WDW!
