My own technique, using Army Painter's metallic paints, is to use True Copper as the base layer, then drybrush over it, progressively, with Weapon Bronze, Gleaming Gold and finally Bright Gold. The drybrushing takes away the metallic shine which you get from those paints, but offers an interesting blend of "bronze" colours and gives a worn look.
I then apply a Strong Tone wash on top, to add contrast.
Gloss varnishing over all this restores the "gleam" effect, if desired.