local Orlando resident here, there's no other way to put it, it's hot. It starts hot and gets hotter, please keep in mind signs of heat exhaustion.
Drink water all day (try and stay away from soda, coffee and alcoholic beverages) maybe a powerade now and then but you should be drinking water frequently, don't wait until you are thirsty.
As much as possible dunk your arms, all the way up to your elbows if possible, where they sell the water fans, those huge buckets with ice in them. I know it hurts but the wrist is one of the places in your body where your veins are closer to the surface of your skin so the cold will go faster through your body.
Bring an umbrella and use it while standing outside, be it in line for characters, or parades.
Try and plan outdoor rides in the morning and evenings and indoor attractions/shows during the early afternoon, afternoon and early evening hours.
Remember to eat, when I'm hot I don't feel hungry at all
I've seen way to many people just out of nowhere faint cause they didn't have a good plan for the heat