Although a guitar (at least most guitars) are made primarily out of wood, you don't want to clean your acoustic or electric guitar with regular household wood polish (such as Pledge). Not unlike a car, a guitar's finish is designed specifically for musical instruments. That doesn't mean you have to spend an arm and a leg on proper cleaning supplies. A good bottle of guitar polish costs less than $10. It is worth noting, though, that different finishes might require specific needs. So, a cheap bottle of Fender guitar polish will work just fine for a Stratocaster with a polyurethane finish, but you might want to get something different for a $6,000 Archtop with a lacquer finish.