First of all, no square elbows. The arms are always rounded and never snap in angles, just curve.

Second of all, the color scheme. Try to make it so that the black lines really do bring out the color (it's so dark that everything gets ruined.)

Third, hair: If you wanna make a split hair, you need to realize it has body, and yours looks like two paper sheets. Make it flow with the shape of the head (like hair usually does)

Fourth: The body is too long (This one goes for you as well, asdf, with that latest guy), and too wide. Body is usually as large as a head, and never wider than it's radius.

Fifth: Please make round ends for hands. The square ends look really awkward.

Sixth: Thicker lines. It's got too thin an outline for it to look good enough.