So you've done all the prep, you've set the table, and now it's showtime.
The GM's Talents
While prepping adventures is a science, running adventures is more of an art. Every GM is going to run his table a little bit differently because every GM has different talents as a showman. You might be more empathetic than you are improvisational, or better at narration than you are at acting. We're each going to possess these skills in different capacities, and that's OK. This section of the GM guide is focused on general tips and tricks that will help you no matter what your experience level.
Empathy
An empathetic GM is a curious GM, always interested in what players want and how their contributions can help shape the fiction. That doesn't mean you're going to give them what they want outright—part of that empathy is understanding that players are players in a game, who also want a challenge.
Acting
The degree to which you're acting in the theater sense depends on how you run your game. Some GMs do voice acting and use voice changers and gesticulate and expect players to do the same. That's a lot of fun if that's what your table is into.
But the acting can also come in how you deliver information from an NPC, even if the dialogue is delivered in the third person. To say "the dark wizard leans forward with gray eyes and says 'She is still alive...'" can be just as impactful as leaning forward and saying, "She is still alive!" and then cackling in that ridiculous Skeletor voice from Masters of the Universe. However you deliver the news, it can also be enhanced by the immersive scene-setting of earlier narration.
Improvisation
No matter what your GMing style, you've got to be prepared to think on your feet. Beyond cooking up NPC personalities on the fly and navigating fictional conversations, you've got to remember the core rules and roll with the punches when the players take the adventure in unexpected directions.
A lot of the muscle memory of knowing what mechanic to reach for just comes from experience over time and a mastery of the rules. But adapting an adventure on the fly can seem daunting. Remember that you already have the tools to shift things around through the structure of scenes or manage the cadence of the adventure by strategically choosing mechanics that shorten time out-of-game.
Narration
This is the storytelling part of running a role-playing game. Borrowing from storyteller techniques is key to being successful at narration.
You are the players' eyes and ears into the adventure, as your narration sets the mood through your tone of voice and word choice. By speaking deliberately and engaging all five senses, you immerse players in the fiction, and an immersed player is better equipped to help you extend it. Your narration is also the glue that keeps the fiction consistent from moment to moment, so building a picture in your head as to what's happening is just as important as communicating it clearly to your players.
Moderation
A talent for moderation is different than a talent for adjudication, because moderation is about exercising your authority to resolve things with fiat, whereas adjudication is about interpreting the rules to yield a ruling that's consistent with the rules.
When you moderate, you move the spotlight from player to player with fiat, you say no to things that violate the premise of the game, or you table conflict coming from a player that might harm everybody else's enjoyment of the game. To be a competent moderator, you have to be confident and firm, but always lead with empathy and the well-being of the table at top of mind.
Adjudication
Developing a sense of fairness with respect to interpreting the rules means figuring out how to put your ego aside and make rulings in a vacuum. This is difficult to do because you also have an agenda as a GM, and sometimes the needs of that agenda may tempt you to fudge the dice or make a ruling so that things are easier for you in executing that agenda.
For a good adjudicator, doing either of those things is tantamount to cheating. The players look to you to be a source of truth in the game, not a charlatan Wizard of Oz who thinks he knows better about what is enjoyable for them than they do themselves. This is why there is no "rule of cool" in OSR+.
Player-Facing Roles
One way to lighten the cognitive burden for the GM is to assign players a role in running the game. Here are a handful of player-facing roles they can adopt that will take some of the work off your hands.
The Chronicler
The Chronicler is a player who's responsible for taking notes on what's happening in each session, so that when recap time comes around, he can relay important adventure hooks that were surfaced during the last session, or refer back to lore that's become relevant to those hooks. An enterprising Chronicler is responsible not only for the narrative trajectory of the campaign, but all the story hooks of all the PCs.
The Cartographer
The Cartographer takes note of where the PCs are and where they're going. Whether that means managing points of interest on an actual map of the world, or keeping track of locations to explore that have been surfaced by adventure hooks, the Cartographer is the player the table looks to when they're not sure where to go next or where they've been.
The Rules Lawyer
Normally, Rules Lawyers are thought of as the bane of the GM's existence, but in the context of a player-facing role, the Rules Lawyer is a godsend. This is the guy you can ask to look up a rule that you don't remember so that it doesn't disrupt the cadence of play. He can keep you honest as you adjudicate, and often keeps other players honest (much to their chagrin), because he genuinely loves the rules so much.
The Caller
The Caller is an old school player-facing role that specifically exists to organize turns in initiative. In old school play, the Caller would coordinate with all the players at the table (there were often quite a few of them back then) and figure out what they planned to do on their turn, then relay that information back to the GM as a single voice.
In OSR+, the Caller just keeps track of initiative on your behalf, and if he's particularly enterprising, he can also help the GM corral them into action or remind them of options at their disposal with respect to their character sheets. In other words, the Caller can be another pair of eyes on the fiction, helping to keep things coherent for all involved.