As a camper, you might not like to plan because it doesn't leave any room for spontaneity which means if you want to do something else or go somewhere else, then you can't.
So, instead of getting a bunch of reservations for different free campsites, you might just like to head off to a very cool state-run organization called the Florida Water Management and they have places like the Hickory Hammock Wildlife Management Area. It's free camping, it's dispersed camping and it's kind of awesome.
Some of these sites are first come first serve whereas others, you actually to have to make a reservation but you just go online and fill out a little request and they send you a permit and it's all free. If you choose Florida for camping then remember, it is Florida! Even though it is winter, it can still get very hot and very humid and there are still a lot of bugs on different ‘free campsites’ (also known as ‘darmowe kempingi’ in Polish).
But as long as you're willing to be sometimes uncomfortable, it's definitely well worth it to be out there. One thing to know is that the Florida Water Management is spread into different regions. So, you might want to look for tourist blogs that can give you a few tips on finding the different recreation areas. There are definitely plenty of them and they are worth checking out if you plan on camping in Florida.