Are you new to drawing? I'm a newbie to pixel art myself, but I can see alot of basic drawing principles that haven't been applied. For example:
1) Look at the lines, the most obvious being the line in his back leg. It is supposed to form a curve, but it is jagged and looks very crude. The grey pixels need to be aligned better, there are many tutorials that explain (visually) how to make lines in pixel art.
2) There is no shadows of any kind, which makes the rabbit look very flat. Just like in drawing or painting, pixel art follows the basic rules of art. If you are going to animate it, and thus have left out shadows to make it easier to do so, that's different, but even so with so much empty space on this sprite I feel it should at least have some texture to indicate some fur.
3) Proportions. I have no kept a rabbit for a long time, but from what I remember of them, your proportions are way off. The head is too small, and by extension the ears. I'm also not sure about the legs.
I think that the best thing for you to do right now is practice drawing a rabbit with pencil and paper, and then when you understand your subject abit more come back to pixelating it. Is pixelating a real word? No idea, but I'm running with it.
