Mirrors are notoriously easy to smudge and streak, and improper cleaning technique can worsen the problem. Using a standard circular cleaning motion can actually redeposit dust, dirt and oils from your cleaning cloth back onto the surface of the mirror, leaving cloudiness and streaks.
Spraying cleaner directly on the mirror can actually allow it to seep behind the silver coating and create black tarnish marks.
Simple Green Naturals Glass & Surface Cleaner uses a naturally-derived formula that is a safer alternative to ammonia and harsh synthetic chemicals.
For best results, use on cool surfaces.