There's pretty much only one one way. Get to the turnpike, go south. When you come to the turnpike extension (Homestead), get on it. When you come to the end of the extension, follow the instructions to US1. That's the Keys Highway and will go all the way to Key West.
You could, I suppose, go over to 95 at Daytona and then go south (or come back that way), but there's usually more traffic on 95 and there's almost no difference in scenery (if you want to call billboards and concrete fences scenery I guess there's a difference).
Expect something like a 5 hourish drive to the end of the turnpike extension (far end) from MCO. It can vary a bit depending on traffic and stops.
-steve