uh i learned this the hard way- 1) Never shade with complete black 2) never use a light resource with complete white. That's all of them really.

try shading with blue! its super fun!

I haven't tried this with drawing guys yet, but drawing the hips first instantly fixed my proportions (on humans at least). Also, draw hair as on thing (don't think of it as a whole bunch of hairs) and then just add some individual hairs at the ends.