The most important piece of advice I have is NOT to try to see and do everything in one trip. We've been with our son 4 times and still haven't done everything in all of the parks. Plan ahead and pick the rides and shows you want to see the most. Also, don't get too caught up in rushing from one ride to another. Take time to notice the little details that set WDW apart from other theme parks.
What the others have posted about the dining plan is great advice. We love it. And I can definitely second the idea of taking a break in the middle of the day, especially if you want to watch the fireworks in the evening. Disney can be exhausting mentally and physically. If you don't pace yourself, you will regret it. I speak from personal experience on that one.
I hope you have a great time on your trip!