I keep noticing that training certain skills improves other apparently unrelated skills. I haven't done much exercise to develop smoother line drawing, but after about two years of animal studies I'm becoming much more confident with lines too.
Geese, ducks, swans (from life)
Cougar (from photos)
I guess that's because most animals don't stand still, so you have to become very fast to draw them live and improvise a lot. This has forced me to rely on less pen strokes to draw the outline. As a result now I appreciate line drawings a lot more. I prefer to sketch animals using more lines to give them a fuzzier feeling but now I alternate the ballpoint pen with thin markers.