I am by no means an expert, so consider this a sort of “peer review”, here is what i think you can improve:
1) I used to also try to do a drawing on paper with a pencil first, as I was most comfortable with that medium, but that never really worked for me. I can see a lot of the detail and definition you added on paper is lost in the colored version, and it would work better if your lineart was on top of that, or if you and more definition; learning to draw lines digitally is difficult, i am still struggling as well, but i think it is a very worthwhile investment. Difficulty also depends on the tablet you use, and how natural it feels to you
2) The other thing i think you can improve is foreground vs background separation and treatment - in your current artwork you have treated both your character and the background in a similar way, so when looking at it is a little difficult to identify your focal point. I would assume the focus is the character, so that should be where most of your detail and effort goes, and the background should be more muted, and less detailed - you can check some character portraits online to see how your favourite artists do this.
Hope this helps!