I'm not sure there is a beginner's guide persay, but I'd be willing to contribute my ideas on what responsibilities a GM has. I think first and foremost it depends on what kind of game it is and what you are looking for in said game. Some GMs like a game structured to what they want and how they want things to go. Other GMs give a more sandbox feel to their game, letting their players direct the game with only a basic concept given by the GM.
In either case, in my opinion, a GM should be sure the game is fair and equal to all players. There should be set rules given so things don't turn into mass chaos, ie if you don't want help moderating then say so up front or if you feel someone might know the setting (if its something canon or otherwise) and you wouldn't mind them helping answer questions, it is a good time to state that as well. Also if you want a set posting rate or posting order, those are two key things people need to know before starting a RP.
The setting should be fully laid out to your expectations and I personally think an image helps along with that in a lot of cases. Templates are a players best friend. Especially those who aren't as skilled in basic coding. Said, template is usually for character sheets (which again are up to the GM as to how extensive they need to be) or even posting.
As for character sheets, I think there is such a thing as too much. I don't believe you should list out every single detail for all the players to see on 'paper'. You would want basics, such as likes, dislikes, appearance, personalities, and histories. Things like favorite foods, ideal mate, etc wouldn't be as necessary i would think. Though again it depends on your game setting as to what is necessary to what you need to make it successful.
There should be at least four starting threads to any group game. An OOC - for obvious reasons, which may later need a separate one for game questions and important matters vs one thread for both IC OOCness and just general chatter. The second most important thread would be a seperate thread for characters and/or game info. Those could be broken up into two threads if needs be, again depending on game size. The third and fourth thread would be IC threads. I fully believe there should always be at least two threads for IC postings at the start. It gives people more choices and doesn't make it so crowded that people get overwhelmed.
Above all else, when GMing, you should never feel as if its a job. You shouldn't dread it. It is supposed to be as much fun for you as everyone who plays with you or under you.
Thats my two cents for what they are worth. I hope it helps in some way. :)