Don't use a polarizer on jewelry (at least not on metalics and stones!), the product should sparkle and shine, not dulled! The one exception is on watches where the glass reflects too much (see this video frompro photo life).

It helps if you know a bit about how the jewelry is supposed to work. For example, rings often have stones set in a way that light is reflected through the stones. As a photographer, you can use that information by adding light from the back so that it nicely shines through.

It is not easy to bring jewelry to life and there's really no standard recepy for all, just trial and error I' afraid...