Paint the skull with silver paint. You may need several layers.
Place the flourish in the middle of the skull at the top. This provides the backbone to your other gem placements.
Draw on swirls and other patterns using a pencil pressed into the skull to leave an indent. You can try to make these symmetrical but you need to remember that the skull itself is not symmetrical.
Cover the joining line at the top of the skull with gems to hide it.
If you have any of the flourish left, use this at the back of the skull to make an extra feature.