Know the Difference Between Smiling and Staring
Yes, elevators are giant dangling yo-yos of awkwardness, but one way to dissolve a little of the tension of traveling in a tight space with strangers is to give everyone a generic nodding smile. It's an effective nonverbal way of saying, "Hi, I'm normal. Excuse me while I invade your intimate space."
The key to a good nodding smile is to keep eye contact to a minimum. After that, shift your attention immediately to something else. Anything else. Your smartphone. The exciting parade of numbers over the door. The scrawled inspection log.
All the more reason NOT to go back for seconds on eye contact. Staring is second only to passing gas on the list of elevator no-nos. The only exception is if you're commenting on something mundane, like your elevator mate's cool earrings or overstuffed briefcase. Then it's right back to the inspection log before things get weird.