It is most important to understand your camera. If you have a Macro setting you may take the picture from a very close position. If the camera does not have Macro, perhaps you have Zoom, to stand at a greater distance and make the picture magnified.
The second most important thing to learn is light. If your light is too bright, the colors will not be good, and the details will be hard to see. If your light is too dim, you will also have problems with poor colors and details. Try to arrange the light filtered, bright, but not making a lot of reflection.
If you practice with your camera, you will learn the best way to take pictures of your jewels.