Like Sofia said, it's good to finish by transitioning down into a walk and if possible let them stretch out their necks and loosen their girth. The aim is to get their breathing for back to normal! Afterwards I always sponge down the saddle area and between his hind legs with one sponge and then his face with another. I always hide down his legs to keep the tendons cool, particularly if we worked on particularly hard or deep surfaces
A light distended trot, hack or walk are good ways to let your horse cool down. I also like to turn out my horse right after I ride him so he can move around and walk freely.