Place a 2-by-4-by-1/2-inch sheet of plywood on your work surface, with the 4-foot side in front of you. Draw the shape of a crown on the plywood, using as much of the plywood as possible. Cut the crown shape out using a jigsaw. If necessary, use a rotary tool to cut out tight angles. Sand the cut edges with medium-grit sandpaper.
Paint the crown with silver or gold paint. Use wall, acrylic or spray paint, whichever you prefer. Let the paint dry overnight.
Attach the crown to the wall where you want the bed. Position it so the bottom edge of the crown is 23 inches off the ground. Use a nail gun to place nails along the edge of the headboard. Place one nail every 6 inches, positioned 1-inch in from the edge. Paint over the nail heads using more silver or gold paint.
Attach faux gems to the crown using construction adhesive. Apply the adhesive to the back of the gems and press them against the plywood crown in any pattern you desire. Hold each gem in place for up to a minute while the adhesive starts to set. Let the adhesive dry for two to four hours before setting up your bed in front of the headboard.