If you've drawn a face before, that will take some time to learn. First you need a drawing anatomy book.

Look at your face in the mirror.... notice your eyes are centered between your chin and top of your head. Your ears and eyes are lined up to the lower ridge of your skull. To start draw an oval with a line down the middle and across the middle, that is where you start with the eyes and everything else is measured from there.

When out in public notice the similarities in the way people faces all look alike.
It take a knack to draw individuals, a knack I don't have while others do. My knack is in still life while other don't have that one.