A writer wants the people who inhabit his stories to resonate with readers. Physical description must deliver a picture that will help make characters, especially the main characters, real in the reader’s mind. You can more readily get readers to invest their emotions in a character if they “see” that character within a scene.
The face will often be the feature that distinguishes one character from another and it doesn’t take a lot of description to give the reader a template on which they can use their imagination to imprint a recognizable face. You don’t need to provide a laundry list for every, or any, character. Don’t talk to the reader like you would a police artist; one distinctive phrase is usually enough. Other features can be delivered in an almost unconscious fashion in the course of the story: “He wiped the sweat from his wrinkled brow” or “A finger brushed the pale scar on her dimpled chin.”
Today’s stretch: In one sentence, write an initial description of a new character’s face.
His flat, round face glowed from the effort, mottled like the bottom of a copper pot fresh off the burner.