Telling an employee that she did a great job just doesn’t help much. If that’s all you do and do it often, it may actually do some damage.
Effective positive feedback is specific. It helps the employee understand exactly what they did that you like so much. It expands their awareness of their own behavior and reinforces it so that the employee is more likely to repeat it in the future.
Need some examples? This article provides four that will help you better understand the concept.