After determining if there's not clear coat. I like to use Busch's Aluminum polish $18 a pint, available at most truck stops. Bush's is a liquid, and works very fast at cutting through the dull. It does not leave as great a final shine as Wenol/Simichrome/Flitz or Mothers mag polish, but it's close.
Quick way to test for clear coat, is gently use most any polish on a small area. If your rag stays clean, it's coated, if the rag turns black quickly, it's not coated.