To be honest, you'll need to improve your sense of perspective and anatomy if you intend to make a full sheet.
As always, I have an edit with me:
The most blatant problem is that your sprite is flat. Well, I mean, it's a 2D picture so it's supposed to be flat, but what I mean to say is that, not only is it flat, it LOOKS flat.
That is to say, it doesn't convey depth through colors and shape as it should.
Here, maybe this will help illustrate:
See how in my edit, the entire sprite is centered at the drawn angle? In yours, however, the eyes have the same width and are right at the center of the head (even though the head is supposed to be at an angle), the logo on his shirt is at the center of the sprite, the arms are almost entirely equally visible and both feet are facing exactly the same direction.
More on the anatomy area, the pose is not stable and certain body parts aren't quite right...
The head is too far back, the legs are too close together, right foot is at an uncomfortable angle, lower leg isn't drawn properly (leg should become thinner towards the ankle)...
Worst offender is the arms, which, as was pointed out, are grossly stiff. The left arm is at a perfect 45 degree angle, which is awfully unnatural. The right hand has shadows on his knuckles when it shouldn't, and that position is not only impractical, but also looks a little painful on the wrist. While we're looking at that area, the sword's blade is facing the wrong angle, and the hilt suddenly disappears on his palm.
The shape of the pants was also kind of wonky, and the hair didn't seem quite like hair, so I tried to alleviate that.
Design-wise, there's not a lot to say other than that his shoes kind of look like tissue boxes.
Sorry if this is a little overwhelming, but it's best if I tell you things as they are. I suggest you go grab yourself some sword wielding poses as reference, and, well, just use references. A lot. Best of luck.