My dad and my brother (the other shop owners of FourElephants) are great with cameras. Unfortunately, we don't live together while I'm away at college, and as a result, a lot of my own item photography has to be done by me in a poorly-lit dorm room with windows that only face north.
Here's a list of tips I've picked up from around the web, or invented myself to help me take treasury-worthy pictures. It's not at all exhaustive, but I hope it helps.
1. Never ever ever ever use flash. It always leaves a shadow and it's impossible to get rid of it without washing out the other brilliant colors of your items. Flash results in pictures that make your item look cheap or your background look too dark like this picture I took over a year ago:
2. Pay attention to what's in your background. Nothing is more distracting to a buyer than a strange object or dirt in the background of an item photo. Because of my unfortunate window situation, I spent a lot of time photographing items on my windowsill which is white and black (not necessarily the best color combination for my felt items). One day, I decided that what I had wouldn't do, and I set out to find a surface near a window that wouldn't compete with the item itself. For me, it was as easy as the top of a bookshelf I could clear off. For you, it might be easier to set up a permanent photo station.
3. Provide a variety of views. It's not just about filling in the five photo slots. It's about offering a slightly different feel for your item each time. I suck at doing this, and I know it's easier said than done. Some of the best jewelry photography can capture both how you can dress up or dress down an outfit with that particular pair of earrings. For photography, some sellers choose to show how a photo looks in a living room, to give our imaginations a kick. It's part of the way we compensate for not being able to have our customers feel our items.
4. It doesn't hurt to check brightness on another computer. For a few months, I thought my shots were sufficiently bright, until a seller in the critiques section said they looked a tad too dark. I checked it out on a friend's laptop, and unsurprisingly, I saw myself staring at a slightly grayer and blander version of the photos I uploaded. It never hurts to check to make sure that your settings aren't affecting the way you display your items.