Good start. I'm not the most qualified person, and my edit isn't great, but here you go.
Here are some things that I fixed/would like to point out.
Color:
-Your shades are too close together. Use more contrast.
-Try to avoid pure black or pure white.
-Try to reuse colors when you can. Even though the color count is irrelevant for modern machines, it will help make your piece more cohesive and will make things easier when you animate if you have less colors in your palette to worry about.
-Try hue shifting to make your colors less boring. If you don't know what that is, look it up.
Generally I shift the brightest shade of a color a bit towards yellow and the darker shades towards blue.
-Your shading makes no sense. Its just a gradient from left to right. Think about where the light is coming from and put the bright parts towards the light source and the dark parts away from the light source. Define the
volume of the shape, don't just color it because its supposed to be colored.
Shape:
-Too many straight lines in the profile. Make his "edges" show a little more volume, make it more interesting.
-His posture is pretty awkward. His arms are too far from his body.
-Assuming his body is supposed to be facing towards the left, make that more clear
-His crotchular region is too large vertically. I just moved his upper body down a little.
Misc:
-The outlines are too dark. I generally don't use outlines at all (most people do). I prefer to define things with value rather than lines.
-Consider using smaller sprites (16x16 or 32x32) before you get too invested with this project. I used 64x64 sprites in the current game I'm working
on and they are a PAIN to work with.
I hope you don't get overwhelmed by this, I'm just trying to be as thorough as possible and offer everything
I know. Don't give up, the only way to improve is to keep trying.