Determine how much time you intend to spend at Disney World. Each park is a short drive from the other, and each takes at least a day to explore. If you have plenty of time, you can see all of the parks easily. If you don't, you may need to prioritize.
Make the Magic Kingdom your first priority. This is the oldest of the four Disney World parks, and most people still consider it the definitive experience. It contains classic rides like the Haunted Mansion and the Pirates of the Caribbean, along with parades and fireworks shows in the evening. If you've been to Magic Kingdom before, you may want to think about other parks first, but it remains the heart of Walt Disney World.
Head to Hollywood Studios if you want fun rides and shows. After the Magic Kingdom, it contains the most rides in Disney World---based on popular movies like "Star Wars" and "Toy Story"---along with an Indiana Jones stunt show, a "Beauty and the Beast" stage show and Muppet Vision 3D. If you have older kids you may want to make time for it as well: They'll appreciate fast-moving rides such as the Rock 'n' Roller Coaster and the Twilight Zone Tower of Terror.
Go to Animal Kingdom if you have smaller children or people who enjoy animals. It contains over 250 different types of animals in habitats resembling their natural environments. A number of rides are on the premises as well---including a roller coaster called Expedition Everest and Dinosaur, which takes you through a prehistoric rain forest---and they're all reasonably kid-friendly.
Check out Epcot if your party consists largely of adults or children interested in something quieter or more cultural. Initially designed as a combination "World of Tomorrow" and international fair, it's earned a reputation for enjoyable yet placid exhibits. A number of rides exist on the premises, but they're all fairly slow-moving. Adults may enjoy the chance to take a break, but kids may get restless ... especially with Magic Kingdom just a short distance away.
