At work, how do you delegate tasks to team members efficiently while you are the supervisor or manager?

This is my first job and I've only worked for about 3 months before getting promoted to supervisor but I don't think doing a good job, especially when it comes to delegating tasks. There are many times when I had to close the store late, and to prevent over working some of the members, I decided to take on their tasks myself, which I know is inefficient. I just don't seem to be good at organizing and prioritizing duties and how to ign them properly. Any help and tips?