Hi, Trisha! When it comes to advanced dining reservations, I recommend that you book as soon as you can. Reservations open up 180 days in advance of the date you wish to dine, and some of the more popular dining experiences (especially some of the character meals and signature dining) can book up quickly.
What I suggest is that you browse the restaurants at
Disney World Dining and Reservations. It will give you a description of the various restaurants and what they have to offer, and it will also let you see what's new since the last time you were there! You can make your dining reservations right there at the website, or you can call 407-939-3463.
Some of the most popular restaurants that you'll find are Cinderella's Royal Table, Chef Mickey's, Le Cellier at EPCOT, and the California Grill at the Contemporary resort. 'Ohana is also popular, both for dinner and during the character breakfast.
I hope this helps with your planning!