Windshield fog is condensation that builds up on the glass because the temperature is below the dew point of the surrounding air. The dew point is a reflection of the air’s temperature and humidity level. High humidity levels and temperature, as often found during the Florida summers (or, let’s face it, all year-round in Florida), mixed with low relative humidity and temperature inside the car (especially when you’re running the AC full blast) can cause the window to quickly fog up. Condensation builds on the outside of the glass. You can use your windshield wipers to clean it away, or slowly make it warmer in the car until the window clears. That means turning the AC off for a bit or even turning the defrosters to warm air.
During the winter, the opposite effect happens. Condensation builds on the inside of the windshield because the air inside the car is warmer and more humid (thanks to your body) than the cold, dry air on the outside of the car. To combat cold weather windshield fog, use the heater to slowly draw the humid air out of the car and replace it with dryer air. Turn off the re-circulation feature, as that will just keep the humid air inside the vehicle. If you need to defog your window in a hurry, the fastest way is to make the inside temperature and moisture level the same as the outside, which means turning on defrosters with cold air or rolling down the windows. This method is not particularly comfortable, of course, and so is best reserved for flash-fogging situations.
Remember that clean windows are less prone to fog — they also help with overall visibility!