Nice drawing! It looks to me that there isn’t very much contrast in your values (the darks and lights). This can kind of throw off depth and flatten the image. One place where you can go darker is on forms that are in front of others like the teeth, and the muzzle. Also, unless you’re going for hyperrealism, don’t worry about drawing all of the hairs. Try and hint at the textures through shadows and form. Hope this helps!