I didn't have much time to be selective, but I chose a shell with little knobs over which I placed the rings. I found a smooth patch of table cloth in the shade and snapped away. Experimented with different ring poses; the items, being so small, tiny changes in angles made a big difference in composition.
I put a white vignette around the whole pic - the corners fade to white - so the real contrasty shades are on the rings, and no say, in the shadow of the shell, which happens to fall in a corner.