Hi Sharron!
The first step is to determine when you would like to go and how long you would like to stay. After that, the most important question is where to stay. Once you know when and how long you are going, then you can plan on what parks you might visit on which day which helps you make advanced dining reservations. Making advanced dining reservations is critical if you want to eat in the Table Service (full service) restaurants at Walt Disney World, especially the more popular ones. You can see some more thoughts on planning a first trip
here.
I recommend ordering the free
planning DVD and watching it with your children to see what looks the most interesting to them. I also recommend picking up the book "The Complete Walt Disney World" by Julie and Mike Neal. It has won eight national awards and is full of color photos. It's a great book for first timers.
You might consider using an Authorized Disney Vacation Planner. They are travel agents who specialize in Walt Disney World, Disneyland, Disney Cruise Line, and Adventures by Disney. There are many out there, including MEI - Mouse Fan Travel, Dreams Unlimited Travel, Small World Vacations, and The Magic For Less Travel. They can help you plan if you don't have time to do all of the planning yourself. I consider myself knowledgeable on traveling to Walt Disney World, and I use the services of an Authorized Disney Vacation Planner myself. My agent has saved my family a lot of time and money over the years.
Hopefully this will get you started. Write back if you have any more questions!