Obviously, wear shoes you've broken in and worn in warm weather outside to test them out. One year I broke in a pair at work and at the mall, but not outsiude. When in the heat, the straps didn't allow my feet to breathe so after about 1/2 hr. at the park, I got bad heat rash where the straps were!
DH and I always spray the bottoms of our feet with a deod./ani-persp and never seem to have any foot issues. I have used moleskin before with a bad pair of sandals, but found that the moleskin kept coming off so it wasn't too helpful for very long.
I always soak my feet in the tub with some sort of foot soak I bring along. Then I dry them off and put an envigorating pepperment lotion on them and let me tell you, this has done the trick for sore feet every time!!!! By morning, you'd never have known they were killing me the night before!
No matter how in shape I'm in or what shoes I wear, WDW always makes for tired feet!