If the gamer is in your group, consider an “apprenticeship” period, where the individual co-DMs with you, and is gradually handed off more and more responsibility. This is an older method, one that is often lost in the face of GM-less games and other avenues of today, but it is also a very personal, one-on-one method that can be quite rewarding. As the Game Master, this can also help reduce your workload, be a chance for someone else to see how things go “behind the screen”, and gain an appreciation for the work and methods behind Gamemastery.
It won’t work for every group or situation, but you might consider it.