Here is an exercise of trying to do accurate likeness. I was asked to do a design featuring former Glory fight champion Joe "Bazooka Joe Valtellini".
So how do you draw his likeness accurately? I had to see observe that his hairline was a little bit like a widow's peak. Also, his lips were interesting and different looking from a normal man's lips. They are thin, but a little puckered at the top lip and fatter at the bottom lip.
Arguably the eyes are the hardest to draw. I drew and redrew it at least ten times. I figured that his eyes sorta have that classic almond shape to them, so I accentuated it.