A good accessory has power. Wearing it makes you feel good, so you might carry yourself in a more confident way, which improves everything about an outfit. This pearl ring by Delfina Delettrez is a good accessory with just that kind of power. It looks good with anything, and can stand alone or be worn with other jewelry piled on. It's a low-maintenance fix for any outfit.
The one thing a ring like this requires is a good manicure.
Similar ring available here.