The sketch you see on the left was drawn by me back in 2006. It was one of my first attempts at drawing dolphins. Back then, I was obviously much younger and had no idea how to get the lines and shaping down, but everyone has to start somewhere. On the right is my latest sketch, which I just finished up today. While I still have a long way to go, the improvement is definitely noticeable, especially considering I've never really been that great at drawing.

I'd say the most important part is getting to know the anatomy and proportions of the animals so that you know where everything goes and how it all fits together instead of having to guess like I used to. Plus, I think looking at other artists' work and the techniques they use over the years taught me a few things as well. For example, I've been told that it helps to start with a basic shape in mind and use that as a basis, and I've found that crescent shapes in particular work great with dolphins due to how their bodies are naturally shaped. Overall, I think I'm finally starting to get the hang of it.