I would advise starting with outlines before anything else. Outlines, without any colours or shades, are a great way to work out details. You have a few outline areas that are not smoothed out properly, and there are details within the sprite itself which are messy and would be solved if you looked at an outline first.
Next is to work on a good colour palette, which you can do without having to apply any colours to the sprite. There is ok contrast between the "light grey" and "dark grey" shading in your sprite, but the reds are much too close together.
Next is to work on a good colour palette, which you can do without having to apply any colours to the sprite. There is ok contrast between the "light grey" and "dark grey" shading in your sprite, but the reds are much too close together.