Running a game at ORC
The following could be considered a "best practice" guide - not just for games running at ORC but in general.
Choosing a System
Here's where you need to self-promote. By far the most popular systems at ORC are D&D, Pathfinder, and Call of Cthulhu. These games are always popular, although GMs may need to be strict as to what particular ruleset mods or PC types are allowed (e.g. PHB only, core rulebook only, etc.). If your game is little known, try promoting it on the forums - talk about it: the setting, the PCs, ruleset, etc. Beginning GMs will often find that some players know the rules extremely well, so they can let these players help provide advice to those less sure of themselves (including the GM). See if there is anyone interested among your friends or societies you are already a member of - even online forums for the games themselves.
Aim for six players. Most games have 3-6 at ORC. That way GMs can cover the occasional absence, without the game becoming overcrowded. Bill estimates that in any game you'll likely lose 1/3rd of any players in the first few sessions as well. You can use the Looking to Run A Game area of the forum http://orcedinburgh.co.uk/kunena/looking-to-run-a-game and also the LookingForAGame PM list on the ORC site for this. Use the ORC Messaging system to contact the list - in the To: field use #LookingForAGame or select it from the Contacts drop-down list. ORC always needs GMs to run.
It's best to talk about the game in the forum and give yourself about a month or so to run up to this. Smaller and lesser known system you may have to go into depth about the settings and rules! Put an event in the Calendar when you're ready. Folk can register for it at that point. The event is also published on the ORC twitter feed (@orcedinburgh, and the ORC Facebook page. There's also an ORC Facebook group.
Talk to folk in other games, or at the occasional pub meets, but don't set out to "steal" players from established games. You can also contact players directly - check the Introductions section of the Forum for new players and send them a PM. Also spread the word outside ORC and get other folk onto the site if they are interested.
When to Run
Weekly or fortnightly works best. Too often and a GM will likely "burn out", and players will often have scheduling conflicts. Too long, and players may lose interest or the game loses its drive and energy (not to mention remembering what happened!). If you're gaming on a week-night allow time for people to get to the venue, especially from work, and try and finish at a reasonable hour. If you're playing on a weekend, try and keep the game to 4-6 hours. Stop at a cliff-hanger moment!
How to run/Be a GM or DM
There's whole podcasts dedicated to being a GM/DM. Most say you need to do x or y, otherwise you're doomed. That's nonsense. As a GM, it's your story. never forget its about having fun. As a new GM you'll forget stuff, have to look it up, make mistakes and 'fess up to them when you do.
Finding a Venue
Always a tricky point to bring up. A lot of ORC games happen at peoples homes, but there's a number of venues to use as well. It's a good idea to check with the owners of these venues regarding bookings, and remember: if they sell food or drink, they expect you to buy stuff there. DON'T bring your own. Bill's web page lists some of these places at https://www.themandragora.com/edinburgh-gaming/ Make sure everyone feels safe in the environment you're playing in - be considerate of boundaries and common courtesy.
Let's be honest here - gaming does not always have a good rep regarding safe spaces and harassment. If you see anything untoward happening, speak out - whether your are the subject of it or not. As a new GM, make sure your players - and venue - are comfortable with certain topics, especially in horror games. Some games may prefer their players (or GM) to have a card they can hold up if a subject is making them uncomfortable.
There's also a forum thread for GM suggestions here: https://orcedinburgh.co.uk/kunena/Community-Specific/14130-gm-tips-suggestions-and-advice-from-gms