I would suggest using a different background for your jewelry shots. While it is good that you are using a plain background, the rough woven material tends to distract my eye from the jewelry. Additionally, there are some specks of lint on the background in the first image. I like either a velvet/velour material (my first choice) or a fleece material (distant second choice) for backgrounds. The material needs to be absolutely clean and free of lint. Additionally, there are other setups besides plain backgrounds to use for jewelry photography.
If I were planning a lot of jewelry photography, I would collect a selection of different background materials. Remnants at a an upholstery store are often good buys.
A second thought would be focus. Focus on your jewelry can be controlled in several ways.
Having the jewelry arranged in as shallow a plane as possible...
Shooting with a small f/stop...
Focus stacking...
If I were going to earn money doing jewelry photography, I would shoot with a full frame Canon DSLR and a tilt shift lens. However, you can certainly do this with other equipment...
Other things to consider are lighting (that is a whole subject in itself) and, finally having a collection of supports for the jewelry; such as wedges which can be used beneath the background material to elevate the piece of jewelry at a certain angle. Often something like this collection might be an interesting way to setup your jewelry images...
http://www.ebay.com/itm/1-Black-Whit...item35c3244cd9
There are many display items for jewelry available on eBay...
I would also purchase a pair of acrylic reflection boards (black and white) which will sometimes enhance the jewelry images.
http://www.ebay.com/itm/White-Black-...item1e69859aae
Many photographers automatically reach for a light tent when photographing shiny surfaces like in jewelry. However, there are many other ways to get good imagery that don't requite a tent.
Light tents can be purchased very inexpensively from eBay and the quality doesn't seem to differ with the price. I would not go through the trouble of jury-rigging a cardboard box into a light tent when a completely folding light tent can be had for as little as this one (less than $15 U.S. Dollars.). This one comes with several colored backgrounds...
http://www.ebay.com/itm/20-50x50cm-P...item4856e4b2a5
Here is a collection of jewelry oriented photo setups which may give you some ideas...
https://www.google.com/search?q=jewe...2F%3B750%3B500
I would peruse high quality fashion magazines and also magazines slanted towards the rich and famous. They will have many jewelry ads with top-notch photography. The in-flight airline magazines often have very nice images of jewelry...
Shooting in RAW with a white balance target (such as a WhiBal) included in your shots is a way to get proper color balance. Additionally, when using the lens corrections module of Adobe Camera RAW, you can adjust for a lot of awkward perspective distortion...
Here are some links which might also give you some ideas of ways to photograph jewelry...
http://www.ganoksin.com/borisat/dire...rary/subject/9
http://www.tabletopstudio.com/?gclid...FSReagodZkydqA
http://www.tabletopstudio.com/docume...hotography.htm
http://www.mkdigitaldirect.com/tips/...aphy_tips.html
http://www.home-jewelry-business-suc...g-jewelry.html
http://www.amateursnapper.com/photog...otography-tips
http://stylecampaign.com/blog/?p=56
http://www.brighthub.com/multimedia/...les/42819.aspx