The most important role for a supervisor relates to the technical side of performing the job for which they are in charge. In my experience, individuals that have been promoted from within and have "put in their time" understand the working conditions, inquiries, and complaints far better than anyone else. If they have been promoted, chances are, they have staying power and above average abilities in regard to the duties and responsibilities required to succeed.
Human relations are a close second and are also mandatory in dealing with today's diverse workforce. Employees want to feel connected to their supervisors; work is where most of their life is spent outside of the home and they need to feel content in their position. This is somewhat interrelated with the aforementioned technical skills. When the supervisor has experienced what it's like to be a laborer, for example, they will generally pick their battles in regard to certain situations that they knew were difficult for them in the same position.
Human relations are a close second and are also mandatory in dealing with today's diverse workforce. Employees want to feel connected to their supervisors; work is where most of their life is spent outside of the home and they need to feel content in their position. This is somewhat interrelated with the aforementioned technical skills. When the supervisor has experienced what it's like to be a laborer, for example, they will generally pick their battles in regard to certain situations that they knew were difficult for them in the same position.