To clear fog quickly, start by selecting the defrost or windshield setting on your climate control system. Turn on the air conditioning, as it removes moisture from the air, and switch to fresh air instead of recirculation. Raise the temperature and fan speed to warm the glass and absorb the fog. If the fog is heavy, crack the windows briefly to let humid air escape. For the rear window, use the defroster to activate the heated grid. Avoid wiping the glass with your hand or sleeve, as this can leave streaks and make the fog return faster.