We strongly recommend that RPGs and LARPs start with a Session Zero.
This is a term for a preamble discussion of the game with the players. GMs/Troupes can lay out the overall thrust of the game, what player should expect in terms of violence, horror, agency, and likely triggers. This is also the place to discuss what safety tools the GM or troupe will be using.
The Open Door Policy (any player may leave at any time) is required by DunDraCon; other safety tools we strongly recommend for RPGs are Lines and Veils, and X Card. LARPs may have additional recommended safety tools. All such tools should be announced during Session Zero, and any discussion players want to have about safety and triggering circumstances are also included. The goal is to give people who are not suited to the game the chance to leave the game. This also acclimates the players to the conditions in which they will play. Safety Tools.