Always use a mild detergent that is specifically designed for use with glass and steer clear of any products that will introduce grit as this can cause scratches.
Also avoid any cleaners which contain Hydrofluoric or Phosphoric acid as they are corrosive to glass surfaces. If cleaning a mirror simply wipe the surface with a few drops of methylated spirits using a damp cloth. Always avoid contact with the silver backing, particularly at the edge of the glass as this can cause damage.
For a spotless surface finish by polishing your glass or mirror using a dry lint free cloth - voila, picture perfect!
If you'd like more information on how to clean glass including specialised instructions for our range of products check out our collection of cleaning instructions.