This is the question I've been asking at least 3x an hour for the past three days.
I think there's a danger in taking your own photos -- I think it leads to delusional thinking. You start to believe your lackluster efforts will slip by unnoticed. You convince yourself the jewel will speak for itself. I'm here to tell you -- jewelry cannot speak so please stop expecting it to talk folks into excusing your photography skills.
Along with this goes the counter yet compatible advice to leave enough around the jewel in the frame so that the art director can crop as necessary. Just 1/8 of an inch in the image but valuable to the graphic artist. Also, as a general rule of thumb it's best not to let the jewel go out of the shot -- there are some rare exceptions though so use very critical judgement.