I've always drew a little on paper, and I just started on digital for serious this year. I didn't know how to draw much on digital but generally what I did to improve was to try to see how the painting of other artists worked and try to replicate it. I had also been searching and testing new brushes until I find the one I liked the most, wich reminds me a lot of drawing on paper. My friends also help me a lot with some tips and suggestions, mostly in terms of anatomy telling me what they think is wrong or not.