Measure the width of your bed frame. Add 2 inches to the total. Cut the plywood to size with a jigsaw or have it cut for free or a nominal fee at your local home improvement store. The headboard can be as tall as you like, and you can cut it straight or cut a pattern out of the top with a jigsaw.
Lay the plywood flat and cover the front with quilt batting. Leave at least 4 inches of batting on all sides. Flip the plywood over, keeping the batting in place. Wrap the excess batting around the edges and staple it to the back of the plywood.
Lay fabric flat and place the plywood on top of it, batting side down. Cut the fabric to size, leaving at least 4 inches of excess on each edge to wrap around the back of the plywood. Staple the edges of the fabric to the back of the plywood. Trim excess batting and fabric from the back of the plywood.
Hammer decorative tacks, buttons or other accessories into the face of the headboard. Space them out evenly, make a pattern or follow a level line around the edges of the headboard.
Measure and mark two spots 3 inches from the top and 3 inches from each side on the back of the headboard. Screw one side of an interlocking slide mount into the plywood at each mark, slide facing down.
Hold the headboard up to the wall where you want it mounted. Check for level and mark the top corners. Set the headboard aside.
Measure 3 inches in toward the center and down from each corner mark. Mark the new location and erase the original corner marks. Screw the other half of the mounting brackets into the wall at each location, slide facing up. Hold the headboard up to the brackets and slide the brackets into each other.