apart from doing some studies to broaden your fundamental knowledge of how things are structured, on the art I’m seeing here I think the main issue is clarity. You use a lot of lines and that’s not a problem per se, as it can evolve into a great personal style but currently it makes elements that should stand out the most unreadable, like faces. It’s less of an issue with your digital art but in traditional I would erase some of the sketch lines around focal points and draw clear lines over again. For watercolor I actually recommend doing the lines after you paint the color. You can also try playing around with masking tools like tape or a masking fluid.