I think for starters what I'd do is practice in stages-- first try to get contours of the subject down as good as you can (that's just the outlines and non-shaded details), that way you might be able to distinguish proportions and whatnot far easier. Even if it's just a stretched oval for the tail, as long as it's proportional, you're doing the right thing for these referenced drawings.
I think you've got plenty of potential to reach the stage of being very wise of proportions, and once you've made a decent way there, try exaggerating tones with shading. Right now it seems like you're trying to be accurate with the subtleties in the tonal changes, seeing how it's all sort of the same. Exaggerate them-- have the dark places dark, and the light places light. Practice knowing the dark areas from the light, and gradually contruct the shading into a nice balance.
Right now what it looks like (besides a bit off in proportion) is a pre-shade for a drawing. What I mean is there's darker tones that need to be added to give the right contrast in the drawing, otherwise it will remain flat.
Nevertheless, great start! Hope to see more :)
