Welcome! You should get a ton of ideas over here.
The first thing is (in my opinion anyway) to walk down Main Street USA and marvel at the sights, sounds, smells, and the amazing castle right in front of you. That is my very first and lasting impression of WDW.
I'm sure there are many others with different ideas. You came to the right place. Be sure to check out mousesaver.com and allearsnet.com also.
You are likely to be overwhelmed on your first trip and want to do and see everything! Thats understandable. But just try to remind yourself that you can return another time. On my first trip, the first attraction I visited was 20,000 Leagues Under the Sea, which is no longer there. I visited it for no particular reason except it was not real crowded our first visit was June, 1981. Try to read as much as you and get a feel for what your group likes. Schedule some downtime if you are traveling with kids; they love to hang around the pool! Research and see if any of the character meals interest you and schedule accordingly. Stay onsite if your budget can swing it IMHO, it really adds to the experience and makes it much easier to return for a nap and swim break in the afternoon (especially in the summer). Prepare for the weather expected at the time of your visit because if you are not dressed appropriately, you will be uncomfortable.
My Rides/Attractions not to miss MK Pirates of the Caribbean, Splash Mountain, Space Mountain, Big Thunder Mountain Railroad, Buzz Lightyear, Its a Small World, Haunted Mansion, Country Bear Jamboree it sounds overwhelming, but some rides are more for the tots (although I love them! ) and some are more for the thrillseekers. They are arranged in Lands, so it is very organized. Ride the train for a quick tour of the park. Leave some time to eat a Dole Whip (sold in Adventureland) to refresh your body and soul! Check out the Crystal Palace, Caseys and the Liberty Tree Tavern for meals (do your checking ahead of time). Know the parade schedule and plan to enjoy that. Window shop on Main Street. Buy some mouse ears with your name embroidered on them. Pace yourself, but enjoy!
Epcot Spaceship Earth, TestTrack, every country even if there are no attractions because they all offer such unique experiences. Select a cuisine you particularly enjoy (or try a new one!) and make plans to chow down! Dont miss Illuminations presented at 9:00 p.m. every evening .wonderful!
MGM Muppet Vision 3-D, Beauty and the Beast, The Little Mermaid, The Great Movie Ride, Star Tours (for the hearty! ), Twilight Zone Tower of Tower, Rock-n-Roller Coaster, Magic of Disney Animation, Indiana Jones Stunt Spectacular. Try the restaurants. Enjoy the character actors on Hollywood Blvd. Play Who Wants to be a Millionaire. And dont miss Fantasmic at night!
Animal Kingdom Kali River Rapids (will cool you off for sure!), Kilimanjaro Safaris, Festival of the Lion King, Dinosaur, Its Tough to Be a Bug. Enjoy watching the baby animals in Conservation Station. Eat at the Flame Tree BBQ hard to pass up once you catch the aroma!