/jp/ - Otaku Culture

I'm an absolute beginner wanting to learn the basics firmly before I move on, so sorry if this is a retarded question..

When you make this initial sketch with a circle and the crossed lines, as pictured, where on the circle do I start the jawline?
I feel like I do it completely at random currently, and my results vary between "so good I saved the piece of paper" and "so bad I crossed it out and shut my sketch book for the day".
Should it start somewhere relative to the eye height?