When working on projects, we break it into small tasks, and use tools like Trello or Pivotal Tracker to manage it and track the flow of tasks. A task is added by me, project owner, and then is taken by the developer. It goes to started, finished, and delivered. At that stage I have to test, and Accept or Reject it. Rejected task gets repeated according to feedback. Accepting it means task is done ofcourse.
Now it's easy and tempting to just tick all that's done as Accepted and move on. Automating the process with minimal interaction with the developers. But this is treating them like machines rather than humans. For all the work they put, the only feedback they get is Approved, or Rejected for those reasons. It is efficient process, and straight to the point.
But every now and then during the day, take a moment to write a simple genuine "Thank you" to the developer, complementing her on her work. It would mean a lot more to them to see you appreciate their effort, and connect to them on personal level.
Won't hurt. Won't take much. Makes a developer's day better... and very likely makes her more willing to produce high results.