Measure your bed's width. Your finished headboard should be wider than your mattress. How much wider depends on the look you wish to achieve. Decide how high you want your headboard and take that measurement from the bed frame up to that height. Jot down both measurements on a scrap of paper.
Cut out a pattern from paper or cardboard, creating different shapes that coincide with your measurements. Decide on the shape you wish your headboard to be.
Place the plywood on a flat surface, such as the floor, or a large table or wide counter.
Trace the pattern onto the plywood.
Cut the plywood into the desired shape following the pattern you have traced. Use a circular saw for straight cuts. Cut more intricate patterns with a portable jig saw.
Lay the upholstery foam over the headboard and cut it to the same shape but 3 to 4 inches larger, and wrap it around the board's edges. Staple the foam into place with a staple gun.
Position the batting over the foam. Cut it into shape but 3 to 4 inches larger. Wrap the batting around the foam and staple it into place.
Smooth your fabric out onto a flat surface, face down. There should not be any creases. Lay the headboard face down on top of the fabric and cut the fabric to the shape of the headboard, leaving 5 to 6 inches extra all the way around.
Wrap the fabric around the headboard, pulling gently to eliminate any wrinkles. Staple the fabric to the back of the headboard. Staple alternately at opposite ends to ensure a smooth finish.
Attach the headboard to the wall behind your bed with L brackets.