For my jewelry business at Peggy Li Creations, there are a few things I *always* try and give to the shopper in the description (and sometimes, when I'm updating my website at 2AM, I forget, but I try!):
1) Length/sizes for items. Describe the pendant size or stone sizes as best you can. I've tinkered with using rulers or coins in my images, but it's a little... tacky? Which brings me to...
2) Images. Images are so important. Try and get the color and scale right. Have reinforcing images -- closeups for the detail, and if you can, a photo on a model. I use a clothing bust ('cause pictures on people are hard!). If I had all the time and money in the world, I'd use people as models, absolutely.
3) Describe the materials used. Don't just say "silver" if it is sterling silver or fine silver. Don't just say "gold" if it is really gold plate, 14k gold, or 14k gold-filled. Find these descriptions confusing? Me, too -- so I often reference other websites and keep a glossary on my website for my customers to understand the differences.
4) Describe the colors. It may seem obvious, but capturing colors in photos are tricky. I like to try and describe colors, especially if I think the photo isn't the most representative of the actual color of the item.
5) Use texture descriptions. Is it smooth? Faceted? Rough? Again, details are often difficult to pick out of a photo, especially of small items like jewelry.
6) Describe shapes. Is it round, teardrop, flat, fat, faceted, domed?
7) Describe techniques. Did you brush it for a matte finish? Hammer in a texture?
I'm learning all the time how to improve the descriptions I have for different jewelry designs, and I will continue to tweak descriptions, especially if there is customer feedback on an item ie "I didn't think it was that ----" and try and cover those topics for new products going forward.
OK, so maybe most people don't actually READ the descriptions. But if they do, definitely give them some information to better understand your design. Think about what *you* like to know about an item before you buy it (especially when it's online!). That will tell you all you need to know about writing good descriptions for your products!