Study anatomy! Even a creature of fantasy must have realistic anatomy in order to look plausible. I suggest studying anatomy and working towards a very definite reference as you start out.
As for the actually Zbrush work, looks very flat and not well formed. Are you remembering to swap between levels to lay down the larger details then move down to the finer details? Looks kind of like you just layed it on as it came to your head, without any thought of refinement. You should try to start getting down the larger forms, then incrementally work in to finer details and refinement.
Don't bother using colours either, you will find textures and shaders to be much more powerful, and considering Zbrush is mainly a sculpting tool, you should ignore the surface finish altogether and focus on the model.