People do their best work when happy.I totally agree. I managed a team of program managers at Microsoft for 6 years. I ended up moving back to being an individual contributor (IC) because I enjoy that work a lot more. But having spent time as both an IC and a manager has given me perspective. And that perspective is that the strongest correlation to productivity is happiness.
The primary role of the manager is as champion for the employee: Understanding their talents and motivations, putting them in situations where they can best use their talents, and giving them the motivations that brings out their best performance. The skill set is more like social worker, therapist, or even coach to relly get inside their head, understand what makes them tick, and generate empathy with each direct report individually. The worst thing you can do it try to treat them all the same.
So in your 1-on-1s with your employees, the single question you should always ask is, "How can I help you be happier at your job?" Or flipping it around, "What about your job is making you most unhappy or stressed out right now, and how can I help fix that?" This one technique, coupled with some quality active listening, will immediately make you a better manager. And, sad to say, it will likely make you the best manager your direct report has ever had.
So the first question you should ask in every 1-on-1 you have is simply: "Are you happy?"