For the former, my two years of HS theatre arts helped tremendously, as did moving into a new city for university where I didn’t know a single person, and having to manage my life. Giving loads of presentations regularly both in school and now in uni helps with public speaking, creating effective notes, and presenting facts in a concise but clear manner.

For the latter, I guess a wide variety helps. Archery, sailing, horse-back riding, martial arts, playing instruments, growing up in two different cultures, proficiency in several languages, as well as my major (historical linguistics) and my minor (economics) in uni all help me understand what various activities or things in the game actually mean.

I guess you could add a third type of skill – writing and/or drawing, which allows you to create good narratives and stories, and to illustrate them for your players to see.

My love for Star Wars has been beneficial in harboring an enthusiasm for all things imaginative and wondrous. It sparked my imagination when I was young. The continuation of my interest has accomplished two things: I have a plethora of otherwise meaningless Star Wars knowledge that boosts role-playing games and I am invincible at Star Wars Trivial Pursuit.

Everything that the above PolSci students mentioned holds true. I also learnt to think on my feet, how to get people’s attention, and how to tell a good story as succinctly as possible.

You also need to know how to motivate people (“Of course you want to letterbox an entire suburb at 2AM!”) — an essential skill to introduce wary new players to the hobby.

Oh, and I can lie with a straight face — something every GM needs to do from time to time. #%o)

I’m a former polisci major, which has led me to intrigue and power play games like 7th Sea. Now back in college, I am an econ major, which has led to a ban in my household on my playing Syndicate Technocrats.

I may never have the opportunity to get mugged myself, but at least my NPC got to use it.

Going beyond the last few hundred years, I’ve picked up as much from general sources [like roman building specials on the history channel, Castle,Cathedral, similar books, and wikipedia] as engineering theory.

But silly pipe dreams aside, I’m actually still in University (I’m not even old enough to drink). My major is anthropology, with a focus along sociocultural anthropology. As THELESUIT mentioned, it’s very inspiring and helpful for coming up with foreign lands. A cruel GM can evoke culture shock among his players!

My two favorite things to focus on as a GM is creating interesting, believable cultures, and what has been a real joy is writing up enough fluff to justify magic from such varied sources as Rolemaster (the primary focus), Vancian, television shows such as FullMetal Alchemist and Avatar: The Last Air Bender, or anything else. Through it, I’ve made a cosmology that I like, and am thoroughly overjoyed at my ever-growing material. (Eight typed pages of fluff with hand-drawn diagrams, and still growing!)

Because of my particular riding experiences (ie, being terrified of horses), I think Riding and Bluff should have skill synergy. People who hear this think I’m crazy, unless they’ve ever seriously tried riding a horse, in which case they generally agree with me immediately and wholeheartedly.

Sailing helps, archery helps, reading every fantasy novel I can get my hands on helps. Psychology and computer programming and all of that come in handy from time to time, too.

Studying classics helps a lot, though it frustrates everyone who tries to DM for me, because if they use a Latin name for something, I know it right away. I’m the only one in our group who knows any Greek, so I can get away with using it. Plus, the classics are full of inspiration.

I acted in HS and Community Theater which has really influenced my ability to get into roles or portray NPCs. I also have a flair for accents which comes in part from this experience.

I left home right out of HS and thus have constantly had to make new friends and learn how to manage and relate to strangers. As a GM I’m not afraid to have new people at the table and regularly invite complete strangers to sit down and participate.

I spent a number of years in the Coast Guard. I wasn’t military like the Marines or Navy, but I learned a lot about command structures, bureaucracies, and even more outrageous accents. I also got to see a healthy portion of the globe. As a GM I know what far off lands look like and what is to be thrust into a land where no one speaks your language. Languages in my campaigns are a big deal – in most there is no common tongue.

I’m also very picky about all things nautical and maritime. I know boat design and how things on the sea work.

After the CG I went to college and got a bio degree in evolution, ecology, and conservation. I tend to pack a lot of ecosystem details and biological science into my worlds and campaign settings.

History and cultural anthropology have always been of interest to me. This gets reflected in the cultures and rich tapestry of my campaign settings.

I’ve been paid as a writer and editor over the course of my varied career, so churning out tons of campaign material is second nature to me. It also means I can be very critical of professionally published work.

My university training is in political science, with a minor in history. That gives me a lot of flexibility in creating power struggles between factions, again making the worlds I GM richer and more believable. It means that in my fantasy worlds, the PCs often run across civilizations with complicated electorates (a la the Holy Roman Empire), loose confederations of city-states (like the Delian league), or even more surprising things, instead of the standard, vaguely English-style monarchies.

Law school didn’t provide a lot of things that are useful for RPing on the surface of it, but nonlinear thinking skills, historical information about crime and punishment, and thinking of legality and rules from a philosophical perspective have all given me a better sense of -why- rules are the way they are in games, and how best to portray rules -in game-.

Overall, I’d say my own history has improved my GMing by giving me a broad variety of knowledge to draw on, but also by giving me a good sense of why system matters, and how best to tweak a system to give the experience that I think the players should be getting.