First off, I love the color of the Shark. In the future I would work on the shading on the teeth to give them more of a 3d effect. First area would be were the Jaw /lip and teeth meet. There should be a shadow under the lip giving the teeth a set back look. Then maybe a little shading in between the teeth so like you seeing the inside of the top of his mouth. That is a start and it would make the teeth stand out a little more, then maybe a shade on the LEFT and Right Side of each tooth to give it the rounded cylinder appearance. Make sure you always spray in light layers and not "overshoot" the shade you are trying to achieve.
With all that said, it goes back to what Gix has mentioned....Practice, Practice and more Practice. Good luck on you're Singing
Oh and Welcome to the Board............................Kwit