This is done by learning what NOT to do.
In time management, it's not just figuring out what needs to get done, it's often figuring out what can be left undone that is critical. Some of the best masters of their time are the ones that set things aside that don't need to get done right now and address them later.
Oftentimes salespeople tend to work on the little stuff or we work on other people's stuff or we work on stuff that seems easier. It's these items that have little impact and severely decrease our productivity (although it fills us with activity) and thus take away from the management of our time.