Reflective objects are tricky. It comes down to controlling light. Avoid flash if possible, and provide light that is even and omni directional. This may require you to use multiple light sources pointed in various directions as well as diffusers to soften the light. There are a lot of lighting products for these purposes, such as soft boxes and shooting "cocoons." Also, be mindful of your shooting angles (sorry if I'm stating the obvious

) With an SLR, you should be able to accurately see how the light is effecting the image, unless you're using flash of course (another reason to avoid flash).
A circular polarizing filter on your lens can help keep reflection/refraction in order too.