Ones to definitely make well in advance if you want them are Cindy's character breakfast (must call early morning 60 days before), other in the park character meals, times for outside seating at Rose & Crown during the 2 hours before Illuminations(as it gives an ideal view and thus gets heavily reserved), times for a couple of hours before fireworks at MK at the California Grill in the Contemporary (it is on top floor and has ideal view of MK and fireworks), and Hoop Dee Doo. Also advisable to make them for resort character meals if you want ideal times. For everything else, it is usually easy to get what you want (as long as you have some flexibility with the time for dinner) by simply calling a couple of days or day before and often just the morning of. Try to at least make them for dinner the day before or morning of as often it is difficult to get in many places at dinner (but not lunch) without a long wait by just walking up.