There's a lot of things that you could do to improve this.  Anatomy is the main issue - his pose looks awkward, the arms are different lengths, the knee on his right leg is too high, etc.

 

Another issue is the lightsource - the shading is inconsistent on the legs, and the skin has no shading at all.  The hair could also use some work.

 

Overall, this isn't too aesthetically pleasing, I'm not a super spriter, so I strongly advise that you closely study some of the sprites in the gallery and try to figure out what it is about them that makes them effective. 

 

Good luck

 

 

Ok.