I tend to use extra fine grade steel wool, followed by a metal polish called 'Solvol Autosol', found in car accessory shops. It's a chrome polish, but is superb on almost all metals. It will easily remove any dulling caused by the steel wool. It's also available from Lakeland Limited (for over twice the price!) under the name 'Maas Metal Polish'.
But when I've finished, I wash the item in hot water using washing up liquid, make sure it's absolutely dry, and apply two coats of 'Diamond-Hard' gloss polyurathane varnish, allowing the first coat to dry thoroughly before putting on the second.
By the above method, even my brass doorhandles, subject to heavy use, stay bright and unmarked.