Using warm water with a soft cloth is said to be the best and safest cleaner for a mirror.
Do not allow water to collect and remain on the mirror edges. When using a commercial glass cleaner, use a brand that does not contain ammonia
Never spray cleaner directly on to a mirror. Always apply to a clean, soft cloth, and then wipe the mirror
Tile, wall, abrasive, or detergent cleaners should not come in contact with mirrors, especially the mirror edges. Certain common chemicals found around the home, such as alkali, chlorine, acids (sulfuric, in pool cleaners), acetic acid (vinegar & cabbage) and ammonia can damage the mirrors.
Use your stove hood fan when cooking. Airborne chemicals, although harmless to humans, can be harmful to mirrors
Ventilate your bathing area when heavy moisture or steam is present. Open a window or use the room fan to remove moisture laden air during and after bathing.