What is a Session Zero?
When forming a group, or on-boarding a new player, it is vitally important to have a “Session Zero”
A session zero is when the group meets up (or has 1 on 1 meetings with the facilitator) to discuss various things before actually playing together. Sometimes this is combined with the first actual session of play, sometimes it is a separate meeting. This is an opportunity to discuss table norms, accommodations, introduce the world and create their characters, and the all-important “NO” “YES” and “OFFSCREEN” lists.
Table Norms: The group should discuss what behavioral expectations/requests they have. This is not about how the characters behave, but the “Out-Of-Character” behavior of the participants. For example, some people might find swearing uncomfortable, or you may limit phone use during session.
Accommodations: you may already have an idea of what accommodations your players need if they are not new clients to you, but it is always good to make sure that people's needs are met.
Introduce the World and Create Characters: This is when you introduce the setting of the first adventure and help the players create their characters. Give the players a basic overview of the fictional world of the game and the narrative premise of the first adventure. Then help your players create/select their starting character that they will be playing as. (A lot of pre-built “starter” adventures include pre-made, ready-to-play characters)
The No, Yes, and Offscreen Lists: These are the most important part of a session zero. This is where the players and storyteller determine what subject matter can or cannot be a part of the collaborative story of the TTRPG. Subject matter on the “NO” list cannot be included in the story of the game. An example is that many groups don't want Sexual Assault to be featured within the narrative of the game. Subject matter in the “YES” list are the things the players are actively interested in participating in. For example, somebody who liked Game of Thrones might ask for “political intrigue” to be a part of the game. Subject matter in the “Offscreen” list is stuff that is not forbidden from being in the game, but shouldn't be center-stage. An example is that a group might put “sexual content” in the offscreen list, meaning that you would “fade to black” instead of role-playing out a scene with sexual content.
Why are the “NO” and “OFFSCREEN” list so important? One of the strengths of TTRPGs is that you can place your players in stressful or emotionally-charged situations in a safe and controlled environment. The degree of separation between the player and their character gives space to process intense emotions by not experiencing them directly. You will want to occasionally push your players into their discomfort zone, and so it is vitally important to know what is or is not “off-limits”.