Have you ever wanted to live in a state where leaving a pair of leather shoes outside in the summer for a couple of days can create you your own mold garden? Welcome to Florida!
There are days, usually in August, where I wonder why we ever bothered taking this, my lovely home state, away from the Indians who had it first. Winters are decent-no snow at least, but summers can be (and there is no other word) brutal. The heat just pours off of everything, and being in the shade only helps marginally. The humidity usually stays upwards of 75%, from June until November, making shedding heat difficult.
One's first urge, which is to remove evey possible stitch of clothing you can get away with and stand in front of a large fan, or lie in a tub of ice cubes is soothing but not ideal as it gives the fleet-sized mosquitos access to tender bits of you that they would otherwise not be able to reach. Note for tourists here-DEET is your friend.
What we who live here have learned is this:
Don't be in a hurry, the slower you move (within limits) the less heat you create.
Wear light colored, long sleeve gauzy type things for shirts if possible. Yes, I know t-shirts are the world standard, but they don't shed heat like very light cotton does. Cargo shorts are also helpful, as they are baggy enough to give air circulation around your legs. Ladies, most of us will not be fashion plates in these clothes, but we will be comfortable.

If you don't have A/C in your home-fans are your friend!
Clean swimming pools are a wonderful thing-it is no accident that there are tons of pools here. Use them, but don't forget the sunscreen. Really, do not forget the sunscreen or you will learn about sunburn in a MAJOR way.
The best idea though is to stay in the air conditioning. We do summer here like Yankees do winter in their home climate. Stay inside as much as possible without going stir crazy. If you don't have air conditioning at home, the price of a matinee movie ticket and a soda will get you a few hours of relief in a comfortable seat-with entertainment, no less.
Lastly-keep reminding yourself that the worst of it is only about four months of the year (June thru September) and that once the heat breaks in September we are well into the swing towards cooler temps again. The humidity will come back down as the sun swings slooowly northwards and those blissful days of 80 degree highs and 60 degree lows are right around the corner.
Good luck and don't forget to buy yourself a tabletop fan!