If you're cleaning up light oxidation and grime, any good chemical polish will work great. Metal polishes usually qualify nicely for this - Optimum Metal Polish is terrific. As is Poorboy's Professional Polish.
If you need to correct scratches and etching, then the abrasives come out to play. I usually start with a finishing paint polish - Megs 205, for example - to see if that helps (least aggressive first). Nonetheless, you can certainly work your way up to compounds and even sanding, as needed. I use a paint sealant for protection afterward.