Hannah - Great question! To narrow it to one skill, I always default to communication. Part of communication is listening, active listening - not waiting for your turn to respond, but listening to learn and understand. We've all done it but once you "hear it" you can't go back. Another part of communication is asking questions. Be the one to raise your hand in a room full of people and ask "can you tell me more so I can get a better understanding?" I have half-jokingly tell younger professionals you need to learn how to read, write and communicate. These all encompass good communication. And like professional musicians who reach their greatest skill level the last day they ever play, it's the same with communication. It is a lifelong skill that will be the foundation of a long, successful career.