Depending on how rough they are it depends.
I usually start with 320 grit wet or dry sand paper (using water ), then keep stepping it down till you get to 1500 grit, then I will use my buffer and just regular paint compound to polish it out.

then go back over it with some polish on a clean buffer pad. it will turn your buffer pads black and useless after doing this.

Oh make sure you go in one direction when sanding as its easier to get the sand scratches out if you go back and forth in one direction.

It will tarnish out in time ,wont stay shiny long if you dont stay on top of it keeping it clean and polished every so often.

Spray