Measure the length and the height of the drawer. Do not include the face of the drawer in the measurement. Use these measurements to purchase your drawer slides.
Pull the drawer glides that attach to the drawer from the larger cabinet member glides that attach to the inside of the desk.
Hold the cabinet members on the inside of the desk. Place a level on top of the cabinet member and mark where it is level. Aim for the middle of the opening.
Attach the cabinet member to the inside of the desk with three wood screws.
Align the slide inserts on the drawer, making sure that they are at the same height as the cabinet members on the inside of the desk. Attach the glides to the drawer with three wood screws.
Slide the drawer into the desk to ensure clearance.