Consider working bigger.
The realistic style that you drew this with seems to me like it's demanding more intricacy. That is, all of the little details that irises encompass, the shadows and highlights that fall onto the eye and the skin around it, etc are missing and although that would be okay if this was a more cartoon-esque or vector style, I think it takes away from a picture that gives off the impression of realism. So, I suggest that you work on a bigger canvas so that you have more room to get in those details.
The other thing that bothers me is the composition. It doesn't feel like there's any rhyme or rhythm to this, so to speak. All of the pieces look as though they're hanging in air. It's as though they aren't parts of a single picture but rather several little pictures on one canvas. Consider scanning it into an image program like photoshop if you can and messing with the arrangement of the objects. They should pull the eye through a figurative path around the picture, if that makes sense.
