I mean like I literally can't get better without vectors. Shaky hand syndrome borks up my mouse and tablet art. I'd have to scan stuff done on layered paper.
if you suffer from shaky hands either:
invest in some software that smooths out your strokes or
turn your mouse/tablet sensitivity way way.... waayy down
it might also help if you zoom in to your work, if use use photoshop, open a second window for overall image view and do close up work with your main canvas and just switch between the two.
Also work at low resolutions since brushes becomes increasingly detailed and complicated (well in photoshop) the higher the resolution. This should reduce some of the detail of your brush strokes making smoother lines.
Lastly if you have a Wacom Intuos 4 (or higher), use precision mode heavily and that will make a huge difference. I love it.