One of the first decisions you'll have to make is where to stay. Hotels off property are almost always cheaper and generally offer bigger rooms. They may even include free breakfasts, although you should ask if that's important to you--for some hotels, "free breakfast" is simply a pastry spread, coffee and juice near the front desk every morning. If you plant to stay off-site, consider renting a car to get around the area and to and from the Disney parks. Some hotels offer shuttles, but they may not run frequently enough to be worth your while.
Disney hotels are generally more expensive than similar off-site accommodations, but offer some great amenities. Staying on Disney property gets you free transportation to and from the airport. Disney guests also get free transportation (buses, boats and monorail trains) to the theme parks and access to "Extra Magic Hours" inside the parks. Disney offers hotels in three main categories: Value, Moderate and Deluxe. There are also some condo-style timeshare rooms that belong to Disney Vacation Club, but may be rented for cash when available.
For many people, the idea of knowing what they will want for lunch or dinner each day several months down the road might sound slightly absurd. However, if you hope to enjoy table-service meals at Disney World during peak or near-peak times, or any time the company is offering a "free dining" promotion, make reservations. You can start to make those reservations 90 days before your arrival date, and many people do. It's especially important to make reservations on that first possible day if you hope to book a meal at a popular location such as Cinderella's Royal Table.
Many people try to plan not only which parks to visit each day, but the order in which to visit the attractions in that park. In general, you should try to visit a park's most popular attraction at the start of the day, as soon as the park opens, to avoid the longest lines. You should also take advantage of FASTPASS, which allows you to skip the bulk of the line if you're willing to return at a later, predetermined time. FASTPASS tickets for popular attractions can run out by mid-morning, so get them early.
A number of pay sites and services can help you create a custom park plan or follow a pre-set plan that has been successful in the past. TouringPlans.com and TourGuideMike.com are two of the more popular options for that level of detailed planning assistance.
It's easy to do just about all your research online. Visit sites such as wdwinfo.com and allears.net for the latest news and information on park attractions, hours and more. There are also guidebooks that can help your planning; either buy or borrow them from your local library. "Birnbaum's Walt Disney World" is updated annually and published by Disney, so it will have all the official information. For the unofficial take--including a more critical approach to the parks--try "PassPorter's Walt Disney World," "The Unofficial Guide" or "The Complete Walt Disney World."
Disney World will send you a DVD to help with your planning--visit disneyvacations.com to get one. The Travel Channel has a host of shows devoted to Disney World, so keep an eye on the channel listings.