Hold a long scrap of MDF on edge against the face of the front piece, flush to one side. Draw a light pencil line along the side of the scrap on the front piece. This will be your guide for drilling pilot holes. Assemble the front piece and one side, held together flush at 90 degrees. Using a countersink bit, drill four evenly spaced pilot holes through the face panel—dead center between your pencil line and the edge—and into the side panel's end.