When you draw heads (realistic or stylized) do you actively use measurements during the process? Do you guess at proportions or do you actively think "okay I'm drawing the lips now and the center line of the lips is 1/3 down from the nose, then the second third is just below the lips, etc..." Especially for other angles I tend to just guess at it and it feels like pin the tail on the donkey as far as placing facial features.

I asked this in the beg thread but I want to see multiple inputs