We are big believers in not doing marathon "forced march" days at Disney. We each pick a favorite thing we want to do on any given day, and treat everything else we do as a bonus. There are a number of excellent crowd forecast websites, that can give you a very good idea of how big the crowds will be at each park on any given day.
Another part of crowd strategy is having favorite low-crowd/short line attractions in each park.
For our family, these would include:
Epcot: Spaceship Earth, Living with the Land, Living Seas with Nemo and Friends, green version of Mission Space, Agent P's World Showcase Adventure, the Tres Caballeros boat ride in Mexico, the Taiko drummers in Japan, and the Impressions de France movie in France. The food is very good in China, the pizza place in Italy, Japan, Morocco, France and Britain. Higher demand ride favorites (which we fast pass) are Soarin' and Test Track.
Hollywood Studios: Toy Story Midway Mania is a great attraction, but absolutely requires a fast pass, even with the newly opened third track. Star Tours is fun, and varies from an easy walk on to a fast pass ride, depending on crowd size. The Frozen sing along show is fun.
Magic Kingdom. Our no wait favorites include Mickey's Philharmagic, The People Mover, the train, Swiss Family Robinson treehouse and the Monsters Incorporated Laugh Floor. The new Fantasy Land attractions, and the famous favorites (Space Mountain, Splash Mountain, Small World, Peter Pan, Jungle Cruise, Pirates of the Caribbean) all need fast passes.
Animal Kingdom. We always fast pass the Kilimanjaro Safari, but in all but peak times, you can usually ride this with a minimal wait even without a fast pass. The Pangani Forest Trail and the Maharaja Jungle Trek are both great, and have no wait. The Flights of Wonder bird show is surprisingly good, and has no wait. Expedition Everest is a fun roller coaster, but requires a fast pass candidate.
While some queues are better than others, it is possible to have a fulfilling Disney vacation which is fun for the whole family without ever standing in line for more than ~30 minutes at a time.