First, I don't use the optimize feature. It has you walking all over the place. I only use evaluate.
I insert the order of the rides I want BY LAND. For example, I'll start with Space, then Buzz, then Speedway. Hit evaluate, then I'll get a sense of how much time it takes. I'll then add fantasyland rides: Teacups, Dumbo, Barnstormer, Mine train, lunch etc, hit evaluate, and get a sense of how much time it takes. Each time I add or change fastpass times so the plan works correctly.
This takes a bit of trial and error, but I feel this method gives me the greatest flexibility in changing a plan on the fly the day of but still having a plan to begin with. As long as I know which land I want to be in at each part of the day, I can fill in the gaps with attractions, and the touring plans maker really gives me a good sense of what I can realistically accomplish in a set amount of time.