The basic rule is this: Anything that someone OTHER THAN YOU can accomplish, even if you don't think they can accomplish it as quickly, elegantly, or effectively, as you: delegate it. You work on only what ONLY YOU can do.
In this way, every task or desired outcome is a learning opportunity for someone on your staff. You decide who. The concern, of course, will likely be the mistakes people make while learning, so here's a fun little, two- (or three-) part, secret to help you deal with that:
Part One -- For any given task or desired outcome, think through how'd you "mop up" should things go terribly, terribly, wrong.
Part Two -- Immediately delegate it to someone as a learning opportunity. (Best case, the delegatee will get it right, saving you precious time. Worse case, they screw it up, but you'll already know exactly what's needed to fix things, which, again, will still save you precious time.)
Part Three (if necessary) -- Mop up. "Yes, Mr. Most-Important-Customer, or Boss, Steve did not handle this as we had hoped, but I gave this assignment, specifically to him, as a learning opportunity. Why? Because I know that the work we do for you is just too important to not have more people know how to get these types of things done for you. Of course learning sometimes results in mistakes, as has happened here, but next time Steve will be that much more ready and able to address your needs if everyone else is busy. And that's the point. In the mean time, here's what I'll do to clean up what just happened..."
Voila! You've settled the matter, can easily circle back to the delegatee to talk about lessons learned, saved yourself a considerable amount of time, and are now ready to do it again (and again) with each subsequent assignment.
You're a genius!