1. Obviously, physical size is a good place to start. Try to express a person’s size through suggestion, not by height and weight. Remember the Cardinal Law of Description: Show, Don’t Tell, or SDT. How large is the shadow he casts when standing up? What could he hold in his hands? How big a cap would he need to cover those ears?
2. Bodily features are crucial, but you have to pick the telling feature or features. For example, if a character is toothless—a key feature because it creates social class—let us see this characterization through suggestion, not by direct statement. Flannery O’Connor, in “The Life You Save May Be Your Own,” creates a hardscrabble old lady through SDT: “He leaned to one side, rooting in his pants pocket, and in a second he brought out a package of chewing gum and offered her a piece. She took it and unpeeled it and began to chew without taking her eyes off him. He offered the old woman a piece but she only raised her upper lip to indicate she had not teeth.” Hands are usually important features because one can tell how hard one works, or what kind of work he does. Fingernails can be dirty or immaculate. Wrinkles are an age-teller. Eyes and mouths are expressive as well.
3. Don’t forget posture and gesture.
4. Dress your characters. Clothes make the strongest first impression in reality and on the page.
5. Include your character’s favorite accessories, or things they carry that reveal their personalities.
6. Let them talk; in particular, let them say characteristic phrases. Use dialect carefully. No corny misspellings; let the bad grammar or faulty usage do the work.
Here’s a lively description of a classic old schoolmarm. Note how, after some physical description, the writer lets her talk: