In order to electroplate plastic you must first make the surface conductive. This can be achieved by the use of conductive paint. Before painting the surface be surface the surface area is clean of items like mould release agent or oils like fingerprints. I would use alcohol to be sure my surface is clean of oils. This will affect the outcome. Best to use gloves to avoid adding fingerprints while handling the object. So lets get down to it. after the conductive paint is applied you first will want to do a copper plating. This will make the nickel plating stronger. After the copper plating is achieved then its on to nickel plating. And finally if you want you can do a chrome plating but usually the nickel plating is enough