I am just now surprising myself occasionally by making sketches of people that look like the actual people I was drawing. I find myself using several techniques while sketching: blind drawing – the drawing of a contour while looking at it and not looking at the paper; converting facial features to their geometrical equivalents and scribing them into the proper place with correct proportions; using tentative, soft lines for facial details.
Each sketch I do uses the steps noted above in various combinations. I have not worked out a formula to go by but rather approach each subject as an individual. I am not always interested in achieving an accurate likeness; gesture, posture and expression are sometimes more important to capture when composing a meaningful portrait.