A simple drawing, highlighted by some soft colour wash in watercolour can be most effective: try it for yourself.
As an Artist, who loves to draw, I cannot emphasize enough, the importance of making a good drawing when starting any artwork.
A drawing is as complex as painting.
To demonstrate what I mean, I have chosen the side profile portrait of an older man. This is a relatively simple illustration but it shows, I believe, the essence of the person without losing this in myriad details of lines, dots or unnecessary shadows. You will note that I have not gone into too much detail in this work as it is the eyes and mouth that play the most important features in the human face.