I have been a Toastmaster since February 2013, and it may very well be the best professional decision I’ve ever made. If you don’t know, Toastmasters International is a world-wide organization dedicated to helping its members develop their speaking and leadership skills. For a relatively cheap price (~$100/year, which most employers will pay for), TM will help you grown your public speaking and leadership skills, yes, but they also develop your ability to think on your feet.
One of the key elements of the weekly TM meeting is Table Topics, in which someone brings a list of questions that you are asked to answer within one to two minutes, without having known the question ahead of time. The first few times can be pretty scary, as you wrack your brain to answer a random question in a thoughtful and organized manner. But then it gets easier, after you do it five or six times, and soon the fear is gone. Yes, it’s always challenging to think on your feet like that, but when you know you can do it without panicking or just saying um over and over again, you become confident in your abilities.
This ability directly applies to Game Mastering RPGs, which is really just a series of answers to other peoples’ random questions based on some loose parameter (the game). When the PCs take your well-planned and strictly-plotted scenario for a ride way the hell outside of where you though it would go (which happens all the time), having confidence in your abilities to go along for the ride without being rattled is a critical skill. And that confidence directly relates to your ability to run the scenario and own the table, allowing the players to thrive in a thoughtful and imaginative environment.
If you are looking for an unconventional way to improve your GM skills, I highly recommend joining a Toastmasters club (there’s bound to be one near you – check the website). For just an hour a week, you’ll be quite surprised.