The Game Master's job might seem like an exhausting one at times. You need to come up with some new, interesting scenario for your players to experience and enjoy on a weekly basis, make sure to pick a day and time to run this scenario that works with everyone's schedule, act as a fair arbiter of the game's rules and mitigate things at the table so everyone remains on track and gets their moment in the spotlight, and repeat the process the following week. You must also make sure to manage the number of players you have in your group and make sure they are a good fit for you and everyone else's gaming sensibilities.
This might seem like a lot to a neophyte Game Master, but there's a simple trick for managing it all, one that's relatively easy to figure out. All you have to do is know your limitations and don't overexert yourself.
For example, I know I have difficulty running games for excessively large groups, which we'll define as roughly containing 9 or more people. I can run for a group containing 8 players, but I'm comfortable with groups possessing 3 to 6, with 4 being my preferred number. Since I know my limitations on this matter, I will refuse to run for a very large group because I know I will have trouble doing so and it will effect my ability to present an enjoyable game to them, which will inevitably effect their fun as well.
You need to figure out your personal comfort level when it comes to several of these things, such as number of players, the game's tone, the length of a gaming session, the frequency of play, and so much more. Knowing this will help you figure out your own limits, and it will make managing those limits much easier. It's difficult to manage something if you don't have an idea of what you're supposed to be measuring in the first place.
Know your limits, figure our your comfort zones, and don't unnecessarily push yourself past said zones. Doing so will make your job as a Game Master so much easier and will take a weight off of your shoulders.
What about you guys and gals? What are your Game Master limitations and comfort zones? How often do you push those limits? I'd love to know.