For me, Refinement means you've got a grasp of the essential basics and its a matter of improving specific skills.
In the case of the drawing you've shared above, it's got solid line work and the rendering (light and shadow) is also serviceable. It does the job and I know what I'm looking at, which is really good! You're at a stage where now "refinement" is needed before the art evolved again as you grow. For me refinement has more to do with technical skill more than personal style.
I once saw a good critique that put into words what I see here. Essentially the rendering doesn't fully match the linework. Sometimes the way in which lines are shaded take away from the lines themselves and muddies up the clarity of the art. A lot of early in their journey artists go through this, I did as well. And even now I'm in a new process of refining my own line work to better suit the way I'm rendering now.
The best way for me to explain this is to show you. Could you share a jpeg of just the linework? Then I can show you what I mean.
Example of my work:(sorry for the low res; it's a screenshot, but hopefully you can see here like how I have less line work in the hair so I can do more rendering on panel 2; but in panel 1 the girl has a lot of lines in her hair, so I don't have to shade it as much to give it definition.)
[p.s. This is two panels from an upcoming comic]