Fill nail holes with wood filler. Let filler dry then sand headboard with 80-grit sandpaper. Fill nail holes again — wood filler can shrink when dry. Sand again, this time with 120-grit sandpaper. Finally, sand with 150-grit sandpaper.
Vacuum headboard with a soft-bristled brush attachment to remove sanding residue then wipe the surface with a damp washcloth. In a well-ventilated area, lightly coat the headboard with spray-on primer, following instructions on spray can. Let dry completely.
Brush on paint, working in the direction of wood grain. Apply two coats, allowing ample time for each coat to fully dry. To distress, rough up edges with sandpaper. Chisel between the plank boards to expose the cracks between the panel boards. Apply glaze to distressed areas and wipe off until desired look is achieved. Spray with clear coat to seal your headboard.