I believe, to make it easy for a manager to manage his time, he should do 2 or 3 tasks he is good in and delegate all other task. Please comment?

If the manager can handle those2-3 tasks at a time, he should definitely take them up and delegate the rest to his subordinates. That would not only manage his time, but would also set a good example of his on the team, and they would work harder to achieve the task.