Useful article from CJ Mahaney on prioritising in ministry/leadership, which may invove saying no to things and delegating but certainly invovles knowing what God has called you for and gifted you to.
First, it is important to understand our roles, goals, and schedules before we discuss responding to unanticipated requests. Often the procrastinator fails to work from biblical roles to establish his schedule, and is therefore vulnerable to the urgent. So he defaults to the most recent—or easiest—request. He neglects the important tasks and is governed by the urgent and the easy. He is busy, busy, busy, but he is not diligent, faithful, or fruitful.
tallandrew 
Very helpful.