You don't sketch like a beginner! My advice would be to limit yourself to fewer lines, resist the urge to use scribbly, fussy lines. You have a natural feel for action and form,give yourself exercises to under 20 lines for instance when you're in a 5 minute or longer pose. If you haven't done so you should practice the facial expressions too, you have what looks like a knack for caricature, and that would be fun to explore!
