This is a question that is asked a lot and for a good reason staying legal will keep you out of trouble. When it comes to Florida legal 35% is allowed for the front driver and passenger door. For the back passenger and back driver as well as the rear window it is 15%. Now for the Front windshield to do the full front windshield it would be 70% (technically clear), or the AS-1 if you would like a strip across the top.
Here is an example of the different shades:
<--70%
<--50%
<--35%
<--15%
<--5% (limo tint)