It gets pretty hot where I am in the summer. Triple digits by June. So after a work out a long walk in the shade is a must. Then they get completely hosed off. If they've really worked hard I pour a little vetrolin or cooling brace into a bucket of water and sponge them with that as well. Some horses get electrolytes in their feed.
Every horse in our barn has a stall fan that's on pretty much starting may and we have some industrial sized aisle fans that keep air moving through the barn. Other then that, not sure what else we can do for them!
I rinse the legs and chest area first. Then I rinse the body several times, scraping off the excess water each time. If you just rinse a hot horse once, their body will heat the water up and actually make them hotter.