Soak a clean cloth in paint thinner.
Rub the paint thinner over the wood to remove the stain or clear finish. Work until the stain or finish no longer transfers to the cloth. Use as many cloths and as much paint thinner as possible but don't soak the wood; soaking wood weakens it.
Let the wood dry.
Sand the wood with 120-grit sandpaper. Sand along the grain of the wood and work until the stain or clear finish is gone.
Wipe the wood with a dry cloth to remove the dust.