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hey artsta, with the profile study, try focus more on the form and making it look 3D rather than the lineart itself, the contour if its drawn in the same width can also flatten the form.

I think you should have a look at some skull pics especially from the side and try and get a feel for the planes and the types of 3D shapes are there.
oh and with your shading- its always best to shade with the form, instead of one direction but shade as though u were going around a 3D shape- just like the top lips in this pic

http://www.portrait-artist.org/pics-ballpointpen-sketch/rendering-lips.jpg

hope that helps man!

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