Ok, here's what I would do:
Get a white piece of card or paper and place your jewellery on it. Set up camp either in front of a window for natural light or position two lights either side of the jewellery. If the camera has auto focus use it as this will work out the correct exposure etc.If you have a tripod use that too as you will get a sharper picture. Experimenting is the best way to learn what is best. Try placing the jewellery on a reflective surface and see how those photos work.
You might find this light studio handy and its reasonably priced
http://www.amazon.co....qid=1271316000&sr=8-8
Once you've taken the photos, download picasa from google, its free and you can play about with the lighting and saturation which will bring up colours. Try not to change the photos too much though as it will make the photo pixelly.
Hope this helps!