Hi! I'm not sure if I really have a lot to offer in terms of guidance as your work already has a lot of very good thing about it. The mood, lighting, color choices and detail work all look pretty good to me. In terms of composition, things look fine too. The only thing of note I really see is some small anatomy and maybe perspective things. So that's probably where i'd put my focus as judging from the 3 images your work is more character centric.
In the first one, I think the neck might be a bit long. The top and back skull might be a bit too large too, unless she has very thick hair.
On the second one, the hands are really small (but maybe she's just made like that!) and I feel like the angle of the head doesn't quite match the angle of the torso.
And as for the last one, the only thing that I see is the ellipses of the armband she has her right arm are just too flat which kills the sense of volume and foreshortening.
Beyond that though, you're doing pretty well I'd say. I hope this helps!