Turn the cardboard headboard over so the back side faces up. Lay it flat on a work surface. Attach two D-rings to the back by spreading urethane glue on the screw plate and pressing it into place. Measure the width between the two D-rings. Install two hooks into the wall spaced the same distance apart as the D-rings. Slip the rings over the hooks.
Cover the back of the cardboard headboard with double-sided tape. Remove the tape backing and stick directly to the wall in position behind the bed.
Screw or nail your cardboard headboard directly into the wall. Position the headboard so at least 6 inches fall behind the back of the bed. Place one screw or nail in each corner. Install two more screws 5 inches above the corner screws.