Measure the width of the door with a tape measure, and divide the overall measurement in half. This is the center of the door width. Make a mark at the center point. Measure from the bottom of the door up to the height where you want to put the hook. Line up the height measurement with the center of the door width.
Hold the hook against the door, lining up the center of the hook with your center mark. Mark the hook mounting holes onto the door with the pencil.
Drill pilot holes with a drill bit slightly smaller than the mounting screws at your marks. If you have a hollow door, use a drill bit that's the same diameter as the hollow-core door anchors necessary to mount the hook.
Place the anchor portion of the hollow-core door anchor behind the mounting hole on the hook, if mounting to a hollow-core door. Thread the anchor screw through the front of the hook and into the anchor. Only thread the screw halfway into the anchor.
Insert the anchors into the holes in the door, and tap the top of the screws as necessary with a hammer until the back of the hook is flush against the door. Tighten the anchor screws with a Phillips-head screwdriver. If mounting into a solid door, simply secure the hook to the door with retaining screws.