Okay, let's begin with the basics.
- Don't be afraid to go off the template, the clothing is stuck to the template.
- Never use pure black in pixel art.
- What's with the shirt going over the hands as well? That's just messed up.
- The way you shade the shirt looks as if your shading off the template.
- The pants, they go over the feet. Be realistic here.
- Your shirt palette is too desaturated, add some blue.
- Your pants palette... Simply horrible. Use the RTP as starters for the palette.
I might have missed something, not sure. Don't be discouraged, just keep trying. ^^
This should be of some use to you.
Legacyblade's Shading Tutorial (Skip most of it, since the beginning is about shading blood.)
There are more, but I don't have any links. Sorry. :\