Wash it first. Then feel it to see how smooth it is. If there are any positive defects, get rid of those first. Make sure it is cleanly trimmed first as well.
Then go over it with #0000 steel wool under cold running water like
BudaFett said. try to go back and forth in the same direction. Buff for a bit, then stop, dry and evaluate. You will know once the shine comes through. Don't go crazy with it, you can always go back and do more, even after polishing. There will be some very fine lines present from the steel wool, the polish will get rid of these (having some there looks good though imo).
Next use MAAS metal polish (the cream, not the liquid!). Apply a pea size amount on one armor piece and spread over the entire piece with a terry towel. Then remove excess with the terry towel leaving a fine coat. Switch to a microfiber cloth and buff in circular motions with good pressure (use your other hand to support the back of the armor plate, not the floor/table). Repeat one or two more times and then clean with cold water and evaluate.
Some people swear by Mother's metal polish but in my experience MAAS worked much better, at least in my hands. If you notice and defects too deep for the metal polish, you can always go back to the steel wool and then re-polish that spot.
