Pretty good, if I may make a suggestion or two (I critique my own work constantly, sometimes manically! LOL) anyways, this is going to sound weird but try to stay away from using lines.... what I mean is to try more shading to point out certain features. It helps a lot to visualize better your main visual goal in each piece.
Also (I still have trouble with this one myself) when drawing body features try to find a way of judging body part sizes compared to other parts. Like when I do a face, I have to envision how big eyes are compared to the nose and mouth.
Hope you dont mind the advice. Keep up the good work!