Only advice I can give is:

Keep sculpting until you are satisfied!

You’ve picked a great subject / reference material — it has some basic shapes, understandable shadows, which are great to start self learning.

Important thing you can do is save your work and do it again in a month or three to examine your own progress.

Another sub-exercise idea, after you will finish this version, try to come up with a totally different color scheme, not present in the reference image — this can help a lot because you will force your own creativity to kick in, instead of just making a copy of something, plus good coloring is deceivingly hard to pull off…