First, given a set of tubes or a bellows, any lens is a macro lens. The results will not differ from those produced by an equivalent macro lens.
In macro, as in 'ordinary' photography, lighting and composition are the important considerations. Your first attempt demonstrates the need to pay attention to both. The central diamond doesn't look to be significantly different than the mounting prongs. The amount of out-of-focus ring structure included in the shot gets in the way, visually. The flatness of the color(s) in the picture add no interest. If the ring is of silver, it should be silver. If gold, gold.
The lighting should be such as to indicate to some extent a 'sparkle' in the diamond.
A good first try, in that it nicely points up some of the problems in photographing small objects.