Lemon juice or vinegar and a scrub brush
Here's how to clean and refinish a wood one
Hot soap and water and a scrubby, let air dry. When you use one for raw meat, wash sooner than later. Do not put wood boards in water to soak. Studies have shown that wood chopping boards naturally kill germs (from their natural defenses against disease). If wood boards are knife scarred, sand until smooth and re-condition with oil.