Use a level to mark each shelf position. Locate studs in the wall with a stud finder. Apply a small piece of painter’s tape to the location of each stud.
Cut cleats to length if not using a store-bought kit from a piece of 2-by-4-inch wood. Measure the space between the outer veneers on the hollow side of the shelf to determine the thickness of the cleat. Measure the width of the hollow area to determine how long to make the cleats.
Pre-drill 1/4-inch holes at the site of the studs. Use a 1/8-inch drill bit to attach the cleat to the wall through the pre-drilled holes. Install a 1/4 inch by 3 1/2-inch lag screw through each screw in each stud.
Test fit the shelf over the cleat for a level fit. Apply wood glue to the inside bottom of the shelf and the top of the cleat. Set the shelf in place over the cleat.
Secure the shelf to the cleat with 1-inch brad nails set approximately 8 inches apart.