Sand the areas around the mirror that you will be applying tiling using a sanding buffer. This will remove debris and will sand down any roughness on the wall.
Vacuum the areas around the mirror and surrounding areas using a shop vacuum to remove any dust and debris from the sanding. Wipe off the wall using a washcloth.
Spread a 1/4-inch layer of fine grout over the area around the mirror you will be tiling using a trowel. Apply the grout in an even layer.
Press small tiles onto the grout, pushing them into the wall to sit at a depth of 1/8 inch in the grout. Space each tile 1/8 inch apart.
Cover the tiles with a 1/8-inch thick layer of fine grout. Apply the grout in an even layer.
Wipe the grout off of the surface of each tile using a washcloth. Leave the grout in between the tiles intact.
Allow the tiling to dry for 12 hours.