Measure the width of your bed and decide how wide and how high you would like you headboard to be. Ideally, a headboard is the exact width of your mattress or bed frame, but it can also be slightly wider or narrower.
Purchase one or more stretched artist's canvases from your local craft store. Select a canvas that, when hung to rest just above your mattress (or even a bit higher), is an aesthetically appealing height and is the right width.
Lay down your drop cloths and place your canvases on top.
Apply the paint to your canvas to create random shapes and lines by using your paint brushes and artist's palette.
Allow canvases to dry. Depending on the thickness of the paint, this might take 24 to 48 hours. Using your picture hanging kit, hang your canvases where you would like your headboard to be.
Using painter's tape, tape off an area on the wall behind your bed where you would like your "headboard" to be. You can be creative with the size and shape, but make sure your taped area is slightly larger than you want your finished headboard to be because the finished product will be the size of the space inside the tape.
Apply paint, using a paintbrush or roller, to the area within the tape to create a "headboard" right on the wall, behind your bed. You could try a faux finish or just paint the area a solid color. You can also skip taping off the area and freehand a headboard if you are confident.
Wait for the paint to dry, then remove the tape. At this point, you can tape off areas within your painted "headboard." Keep applying paint and create a color-blocked effect or other design.