I have got alloys that have a mirror polished lip, I usually wash the alloys with car shampoo, then dry the alloys. If they are really grimy I use Autosol metal polish to get the brake dust off, then I use Autoglym alloy wheel protector (its a white spray can). I recommend the Autoglym alloys protector as it puts a nice polish on the lip and when the brake dust builds up again, I can easily wipe them clean with a tissue/rag.