Some simple things that helped us get the most out of our days despite the crowds:
1) Get there before they open. The lines are much shorter that first hour or two.
2) If it rains, take full advantage of it. Most rides remain open and the lines are far shorter.
3) For the first ride, pick something without Fast Pass that will have a long line later in the day (Nemo, Peter Pan, Materhorn, etc.).
4) Accumulate Fast Passes every chance you get. Send a runner. Some Fast Passes run out earlier, so grab one of those first before they're 2+ hours out. (Maybe have the runner skip the first ride to get Indiana Jones or Space Mountain FPs.) Keep in mind that FPs for the two parks are not connected (and Roger Rabbit isn't connected to anything) so you can actually have concurrent FPs for DLR, DCA, and Roger Rabbit.
5) Use accumulated Fast Passes during the busier times.
6) Fill in the time with some of the rides that have shorter lines or rides where the wait is worth it to you.
7) If part of your group heads home for a nap, leave the passes with someone else in the group so they can accumulate FPs.