Reducing the amount of steam in the bathroom minimizes the potential for fogging.

Turn on the bathroom exhaust fan before starting your shower and leave it running during and for at least 15-20 minutes afterward.
If you don't have an exhaust fan, open a window slightly (if weather permits) or leave the bathroom door ajar to allow steam to escape.
Ensure the exhaust fan is clean and functioning properly.

N/A - Addresses the root cause (excess humidity) rather than treating the mirror surface.

Improve Bathroom Ventilation