Remember that your jewellery is made of an alloy (a mix of metals) that contains copper and it will eventually oxidise over time developing that dull and darker colour that is typical of antique metals. It will also leave dark marks on your skin. Don't worry, it is normal.
If you love that vintage and worn look (like we do) then watch your piece ageing slowly.
If worn metal isn't your thing, then you can treat your piece the way you would do with fine jewellery: store your jewellery in a dry, dark place (such as a jewellery box) and polish them frequently with a specific soft cloth.
Wear your pieces after applying perfume, creme, make-up and avoid contact with water.
If your jewellery is plated please note that plating is a temporary treatment, and sooner or later it will come off.