Could you tell me what kind of pencils did you use? HB and things like that (I'm not really good at shading)
For the darkerst part Ive used a black pilot pen ,a B8 graphite pencil and a B6 aquarelle pencil.
For the other parts I think Ive used HB ,B2 and B4 graphite pencils.
To improve your shading skills you have to practice a lot and also you should try smudging with a paper tissue.
Good luck! ^^
OMG! It's amazing! Can't wait to see it finished *w*