I'm going to leave the first picture alone because I am lazy. But as for the second picture, the shading on the face is nice enough, but it would be about a million times more impact-ful *haha...* if you inked the whole picture, and THEN applied the shading with screentone *but who can afford that? :P*
Here's a big tip, USE guide lines, the person looks like he's slanting at an un-natural angle, making it painfully obvious that you are not a professional (and there is nothing wrong with that). Just draw a line extending from the head to the body *like an enlongated spine* and make sure to keep everything straight or crooked to the extent that it is still believable. The shoulders, are sloping too much, you probably want to use a reference picture or look in the mirror to see how normal shoulders behave.
Make the neck a bit thinner *like 1 mm* If you want to redo the picture, make sure that the hair looks sharper *use more lines if you want detail*arrang the lines nicely however*, but use less lines of you want to define a solid and defenite shape for the hair*
The shading on the hair is toooo dark, its like he has an incomplete bleach job, just erase the shading a bit.
If you want to redo the picture, I suggest you using a light box and copy over the picture using a mechanical pencil (.05 works best) or just redo the picture in .05 so it looks cleaner and less "rough."

Happy drawing!