To clear fog inside your windshield, start by pressing the front defogger button or directing airflow to the windshield vents. Turn on the air conditioning, even in winter, as it helps dry the air. Set the temperature to warm, as warm, dry air clears fog faster. Switch off the recirculation mode to allow fresh air into the cabin, and open a window slightly for a few seconds if the fog is heavy. These steps should clear the fog within seconds, starting from the bottom of the windshield.