To keep your windshield from fogging up in the winter turn off your recirculating feature on your heating controls in your car.
Turning off the recirculating feature on your heating in the vehicle will bring in cooler drier air from the outside which helps to keep the windshield from fogging.
Also you can smear some shaving cream on the inside of your windshield and then wipe it off which helps the inside of the windshield from fogging up.
Another thing you can do to prevent your windshield from fogging up in the winter is to let some cool dry air into your vehicle by rolling your windows down a little before turning the vehicle off for the night.
The cool dry air will help keep the windshield from fogging up.
Just leave the windows down for about an hour and then be sure to roll them up again before going to bed.
Also turn your defroster on while the car is heating up which should help get rid of any window fog in the morning and sometimes you may need to use a paper towel or washcloth to wipe some of the fog away on the windshield which is what I have to do.