Lately I posted some portrait sketches on my instagram and got a few questions by email on how I draw them so quickly.
Since I never went to art school I developed my own way to setup a face sketch in 5 steps.:
STEP 1: I always start my setup with two circles. The one above is a circle to define the brain containing part of the skull. The one below is the one to define the chin.
STEP 2: The next step I draw 2 lines in the middle of the setup. The horizontal one determines the position of the eyes and the position of the ears. The vertical one is the axis of symmetry.
STEP 3: This step is the most important one. In this step I add a couple of extra construction lines. I divide the part below the 1st horizontal line into 2 parts with the nose line. This line will determine the position of the nose. Next I divide the part below the nose line and the chin line into two with a line to position the mouth. Important here is that you draw the eyes below the eye line, the nose above the nose line and the mouth below the mouth line. The space between the eyes is mostly as wide as the nose.
STEP 4: Before I really start finishing the sketch I add a couple of details like the cheekbones, the jawbones and the chin.
STEP 5: Once the previous steps are done you can start focussing on details to finish the sketch. I usually add some more detailed sketching lines and add depth by crosshatching.