As David Hockney once said: "Place the eyes first, the side of the nostrils, the side of mouth and the rest follows". In short, to draw a portrait with appropriate proportions it is mainly a matter of placing a few essential points on the canvas.
This is the technique I use.
First I draw an oval shape. The contour of the head.
In the middle of the oval, I draw an horizontal line. On this line I draw a first eye. Let's say the eye on the left. Then, I place the second eye. The one on the right. I respect a distance of one eye between each eye and I draw the pupil in the center of each eye.
Once the eyes are placed, I draw the nose. The tip of the nose is located a little less than