This would be a similar process to finishing any painted surface. Progressive through the grits, each time removing the scratches from the previous grit, wet sanding with the higher grits. You can then hand polish with polishing compounds you can get at any hardware/car accessory store. You can start with an orbital sander or a belt sander of some sorts. I've done this on guitars I've built.

If you're fairly close it shouldn't be a ton of work.