Polishing a valve cover

I want to polish out my mazda valve cover. I know i can get some polishing wheels for my airtool and some polishing compounds. But do i need to sand it, or prep it in any way before i start the polishing process?

the valve covers I have messed with I took a fine grit wire wheel to first to get them smooth. they turned out alright for me not having much experience. just my 2 cents

If not already, I'd say get all the paint and grease off them first.