/ic/ - Artwork/Critique

I tried copying this but I couldn't really get the proportions right. I just tried following the contours, but without taking any measures. Then I drew a cross in the middle of the face and I tried getting more accurate measurements with a ruler and the tip of the pen, and this time at least it resembles the reference, what's the right approach for copying? should I try to use an aid like drawing a few lines on the reference and then make precise measurements with the pen or the ruler? or should I work more on drawing the contours accurately only from what I see? I don't really know if I should try to draw as accurately as possible. I'm worried that I'm not or actively concentrating on the drawing if I use too many measurements, and I end up not really learning anything.