The shade is always a good 10 degrees cooler. Duck under trees and overhangs. Jungle Cruise is usually a bit cooler with the water being cooler than the air's 100 degrees, but it can also be slightly more humid.
Not going is by far the most effective.
If one has to go, go early and go crazy on all the outdoor attractions (like Matterhorn and Big Thunder and Tom Sawyer Island) until about 10AM, then slow down a bit, shopping in indoor places, riding indoor attractions with indoor lines (Indy, if they ever stop the Fast Pass and use the whole immersive and A/C'ed queue), waiting inside two hours for ice cream on Main Street, going to DTD for a longer than average lunch, etc., until about 5PM when the weather starts cooling down. (And all this time, trying to get fastpasses, so you can get on some attractions at night without waiting. (Screwing up the FastPass logistics in the process, as required.))
"Here You Leave the World of California Today and Enter the World of, um, er, California Today."