The people who only ride 2 or 3 rides a day arrive to the park a few hours after the park opens, have no idea what they should do first, and do not understand how the FP works.
If you have small children, for Magic Kingdom, you need to head directly to Fantasyland -- do not stop on Main Street for characters before you arrive at Fantasyland. We don't stop for a morning picture in front of the castle. We do that a little later in the day.
Dumbo won't be open when you go, so you should go to Peter Pan first then just do all the rides in FL, then you can decide to go to either Tomorrowland or Frontierland. If you go to Tomorrowland, grab a FP for Space Mountain or Buzz. If you are planning to ride both, definitately get the FP for Space first. This can usually get done before lunch as long as you get there when the park opens.
If you head to Frontierland, grab a FP for either BTMRR or Splash Mountain. If one of those has a short standby line you can ride one standby and get a FP for the other.
If your children are older and you don't need to do the Fantasyland rides, then you can start in Tomorrowland or Frontierland.
At Epcot -- head straight to Soarin or Test Track to get FP.
At DHS -- head straight to Toy Story Midway Mania or Jedi Training whichever is more important to your group.
At AK -- head directly to EE or perhaps the Safari.
As long as you at least have a plan for the first few attractions and you arrive either at rope drop (or you can do a couple of days where you don't arrive until late afternoon or evening when people are starting to leave) then you will be fine.
Don't plan so much that you feel rushed and aren't enjoying yourself, but just go in with a some kind of framework for the day.