Mounting a mirror is becoming more common as bathrooms in small locations force designers to experiment with small corner sinks. Installing a mirror in a corner is actually not very difficult and most home owners can hang such a mirror successfully. It is actually more difficult to get used to how the mirror looks once it has been installed.
Measure the width of the mirror. Transfer that measurement to 1-by-1-inch wood and miter cut away from each mark at a 45-degree angle. Cut two boards.
Determine the height you want the mirror and make two small marks on one side wall showing the top and bottom of the mirror.
Place one board 1/4 the height of the mirror from the bottom mark and screw the board into the wall using four long screws. Place the second board level with the first and 1/4 the height of the mirror from the top mark and screw the board into the wall using four long screws (two on each end).
Position the mirror at the marks and place small L brackets to mount from the back of the mirror frame to the top of each board. Mark four locations.
Screw the L brackets into the back of the mirror frame using a power screw driver. (Use the shallow screws so they don't penetrate the frame.) Place the mirror on the boards and screw the L brackets into the boards using the screws that came with the brackets.