Hi Angel. Taking pictures of jewelry is a trial and error learning process, that really is dependant on your equipment capabilities, however, there are a few little tricks you can try:
When using a flash try putting various 'house-hold filters' over the flash, such as somewhat transparent and/or light colored plastics and cellophane’s, or even used stockings (think outside of the box... shower curtains, old sun-glass lenses, that pizza wrapper you have not thrown away yet). The key is to experiment. These 'filters' actually will diffuse a flash and help to reduce glare spots, but keep in mind this will change the light in general, sp play around till you find something you like. You can also get a little tricky and use white card stock (or the backs of old christmas cards...) to 'bounce' your flash into a white wall next to your subject so the flash doesn’t hit the jewelry directly (which is the biggest cause of glare).
If you decide not to use a flash make sure your camera is set on the manual setting and the lighting options are set for the lowest light options... 'cloudy' or 'night' icons are the menu items you are looking for. ALWAYS try to use the manual settings on your digital and explore all the options so you can get the best exposures. Automatic settings are the most limiting as far as lighting and will only 'read the light that its sensors pick up, so even window lighting can be missed by the auto settings.
And just a side note… if you have a scanner, try scanning your items... because truly, that’s the easiest fastest, and highest quality method for making an image of smaller items such as jewelry. Try it, and the headache of trial and error pictures just ‘goes away…’
Good luck!