My resort tips for first timers:
The very first time you go to the food court, buy a refillable mug. You can save a lot of money, even just by grabbing a coffee to go on your way to the park.
Try to visit the food courts and restaurants of other resorts (easy if you're staying at the All Star Resorts, which are within walking distance of each other) Each one has different offerings. They are also less crowded than park food courts, so eat at one if you're between parks rather than trying to catch a meal at a crowded park.
Get a card holder for your Key to the World (KTTW) card. Use your KTTW card for everything.
Familiarize yourself with what is available at the resort gift shop - you will feel silly if you go outside "the world" just to get something that was in the gift shop all along.
Spend time at your resort, especially if you have kids. My daughter says that being at a Disney Resort is like being in Disney World all the time. All of the resorts have childrens' activities. Just hanging out the hotel would be a great vacation for most kids.
As soon as you check in, walk your family around to the places you need to find, using your resort map. The Disney Resorts are HUGE compared to most hotels.
My park tips:
As soon as you get to a park, rent a locker. Unload whatever you can do without for a few hours. Don't plan to go back to your car for things -- it takes too long. This isn't really even an option at the Magic Kingdom. Keep your receipt for your locker rental (I keep it with my KTTW card) so you can get your deposit back and so that you can get a free locker rental at another park if you park hop.
Make a note of where your car is parked. I actually write it on a piece of paper that I keep with my KTTW card. Remember, the parking lots are so big that they have trams to take guests from their parking space to the front gate.
Park hop if the park you are in is so crowded you are no longer having fun. Epcot can have huge crowds but not feel crowded. The others can feel so crowded that you can't move. We have left Magic Kingdom to go to Epcot for a few hours and returned to find most of the crowds gone.
Afternoon naps are important, not just for rest but because parks are often most crowded in the afternoons.
Change your shoes throughout the day to avoid getting blisters. If you do get one, take care of it right away.
If you're travelling with kids, don't do Disney as if you're never going back again and absolutely must see everything. Let them go on Space Ranger Spin 5 times in a row if they want to. I have yet to go on Pirates with my daughter - we're just saving it for next time.
If you must buy souvenirs, try to get something that will last for them eg. a sweatshirt that will fit for a few years, not a few months. You don't have to buy everything on your first trip. We decided to buy Disney shirts on our first trip and mouse ears on our 2nd trip, and just brought them back with us.
My number one Disney tip? If you have a little girl, let her wear a princess dress everywhere that she wants to in Disney World (you might want to have a shorts and shirt under, but still, let her wear it) Where else can a little girl be called "princess" every day?