I think that you need to focus first in the form and then in the detalle. Even though you want to just express it in lines, you need to think in the volume of the head and simplifiying it with forms. For this i would recomend first studing how to draw a box that looks and feels right, then rotating. After this you have to study how to construct the face features and the size and position between then so you can put it all together. After a lot of practice you will be able to stylize it. | Artwod Feedback