| Windex is a good choice. Apply to a clean, soft rag and wipe on and buff off. Heavy duty schmutz will respond to either naphtha or alcohol. Follow up with a coat of Dunlop 65 polish if you wish.
Soap and water used judiciously work in a pinch.
N.B. Avoid alcohol, lacquer thinner, and acetone on nitrocellulose lacquers and/or French polishes. These solvents can dissolve the finish. | 
