I don't draw faces very often, but I've taught about drawing them using proportions. For a straight on view which is what I did, the eyes should run along an imaginary horizontal line about half way from the top of the head to the chin. Usually there is about one eye's width between the eyes. The nose should run straight down between the eyes, and the lips usually fall halfway between the tip of the nose and the chin. I didn't show ears, but the top of the ear is typically even with the eyes and the bottom of the ear is even with the end of the nose. Of course, each persons face is different, so the proportions are only a guideline.
The person I drew came from my imagination. I tried to draw using information I have practiced before, such as lighting, shading and the structure of various facial features. The expression on the face looks tentative to me. I like that it came out that way, because I was uncertain about the music- mostly sung in Italian lyrics. I was also tentative about the sketch since I wasn't using a visual reference. One wonderful thing about the habit of sketching is the more you do it, the braver you get. It's fun to try things outside your comfort zone.
Sketchbook Exercise: try something new this week!