Place a small level on top of the shelf and hold it onto the wall in the desired location. Check the bubble at the center of the level to ensure that the shelf is straight and that the brackets are in the correct spots. Hold the shelf in place with one hand while using the other hand to place the screw and operate the screw gun.
Slide the tip of a self-tapping screw through a hanging bracket's pre-drilled slot. Screw the fastener straight into the drywall using a screw gun until the fastener hits the metal stud.
Push the back of the screw gun firmly to allow the tip of the self-tapping screw to dig into the metal stud. Hold the screw gun as stable as possible to prevent the self-tapping screw from slipping across the metal stud under the drywall.
Stop threading the screw into the wall when the tip of the self-tapping screw penetrates the metal stud material. Continue threading the screw into the wall until its head is near the shelf bracket.
Check that the shelf is still level. Insert a self-tapping screw into the opposite shelf bracket and thread it into the wall. Repeat the drilling process, allowing the tip of the screw to penetrate the metal stud. Thread the screw into the wall until the shelf bracket is pressed firmly against the wall material.
Tighten both screws so that the shelf is set firmly against the wall.