ahhh sketchbook! I used to use that all the time!
tip: the pencil is by far your best tool, you should use it for most of your work
also
u need to stretch out the face I think a bit and make the geometric lines more perfect, also, I'd clean all the scratchiness up and pic tones for each piece of the head (even if things are the same color on the head, the light will hit them with dif tones, so I'd add those in (by blocking) and then shade and blend. good stuff though