It is my belief that a good GM is very important in a Diplomacy game. He or she can watch for cheating, and ensure that interest in the game stays high among the players. In addition, the GM will be performing duties including granting deadline extensions and handling votes if the players want to change any of the game settings. Draw votes are handled by the Judge. All GMs need to know Judge operating procedures and be familiar with all the Judge helpfiles, HTML versions of which can be found here, particularly those files dealing with GMing procedures. In addition, each GM should develop a set of house rules he or she feels comfortable with. You can use my house rules, which can be found here.
The best available GMing guide, however, is Dean Gordon's GMing Guide. I highly recommend that all prospective GMs read it over. If you are a new GM, you should moderate a couple of games for experienced players to get your feet wet before tackling a newbie game. If you need further advice or help, feel free to e-mail me. You can also read my Abandonment Free GMing article.
My best advice to newbie GMs is to simply stay alert and get to know your players. You want to foster a sense of responsibility, so that they submit moves on time and the game doesn't drag on. Don't be afraid to privately and politely remind a consistently late player to submit moves on time. If the situation is really bad, you can expel a player from your game, but this is hard on everyone and is only a very last resort or a punishment for cheating.
I've GMed more than twenty-five Judge games, and each one was totally different. I personally find newbie games to be the most interesting, since it's neat to see the different perspectives new people approach the game with. Of course, it's also a lot of fun to watch top-flight experts compete. I strongly advise GMs to use the "set all press" command in full press games, and watch the negotiations progress. I've learned a lot from this.
If you're interested in joining the Rannestad Convention GMing group, founded to foster responsible play, please see my article on the subject
