I'm pretty new here as well, but I'll help you out as much as I can.
The main thing is that those lines are extremely heavy. Try to define things more with shading than with black lines.
The shading is pretty rough around the edges. It could just use cleaning up in general. There's a lot of places where it escapes his outline or where the background isn't even colored over. It also seems like you're just doing a gradient from one side to another and not paying a lot of attention to how light would actually react on his features.
It would help if you told us what you are going for... if you're going for realistic, the proportions are way off (legs are too short, arms too big, etc.). It looks like you're going for something more stylistic here, but context would help a lot.
That having been said, its not a bad piece at all. Your shades have good amount of contrast between them, with is something a lot of beginners do wrong. The colors aren't eye wrecking like my first few pieces.
His form is good. I like it, but it could use some work.