Give the employee a sense of control over what they do and how they do it. Show them how to deal with customers but let them do it there way to. It is surprising but many people push their selves harder than a boss can push them. Let them give input and contribute to the situation. The third is to personalize the work place.
People spend more time at work than anywhere else during their awake hours.
By allowing the worker to have a voice in the work environment, will let them express their selves which will add to emotional well being, and lower their stress. The last is to look at the overall environment. Let the worker control not only the immediate work environment, but also the temperature, lighting, ventilation, and noise in the surrounding area. This may not be particle in all situations but try to give the employee some options. This is a basic overview of how a manager or boss can get more out of the work place.