Car windows typically mist on the inside if the pollen filter is clogged or if the recirculation is on (i.e. no fresh air).
If you leave the A/C compressor ON, it will de-mist much faster, as the cooling process also extracts and eliminates the humidity from the air. This works even in cold temperatures, when you want heating, because the outside air first passes through the A/C vaporizer, it is cooled, the humidity condenses and drips out of the cabin, then the air passes through the heater core to obtain the temperature set on the panel.