If you are tasked with supervising or managing others, the most important work you do is people building.
While the formal definition of a manager's role focuses on getting work done through others, that overly simplified definition leaves out the longer-term necessity of people development. As you are getting the work done through others, you should also be equipping them for higher level work in the future.
Continually expanding the capacity of each individual and, thereby, increasing the capacity of your team, is the hallmark of an excellent manager and leader.
While it is true that you must ensure that your team completes short-term work assignments, this should be done simultaneously with preparing long term for future work they will need to do.
For many managers, the greatest barrier to people building is that they choose to do the work themselves. They are unwilling to delegate or unable to trust those around them with next-level and emerging tasks and responsibilities.
When the work of people building is not viewed as a key responsibility for all managers and supervisors, a team is inherently limited. What's more, the manager is also limited. You see, you will never have a chance to grow and develop so long as you are saddled with the same work you do today.
Start small if you must. What one task could you give to someone else with the express purpose of helping him or her to develop new skills?
It's that simple. A little bit at a time, all the time, will help you build the people around you and build your own skills, too.