If you are like most managers, you were promoted to your position because you were proficient at you job. Top salesmen get promoted to sales managers, top engineers get promoted to chief engineers, top accountants become partners in their firms, etc.
To stay proficient at your role as a manager, you have to make the shift from getting things done yourself to getting things done through other people. There are a lot of competencies you must master in order to be successful at this and at the same time, it can be narrowed down to just three. They are your ability to lead, to delegate and to choose your team.