Session Zero
"Establish boundaries. And if anyone crosses them, speak up. If they don't listen, there's always cloudkill." - Tasha
Then it goes on to say in more serious terms:
"...session zero... to establish expectations, outline the terms of the social contracts, and share house rules. Making and sticking to these rules can help ensure that the game is a fun experience for everyone involved."
and then the important stuff:
"Often a session zero includes building characters together.
As the DM, you can help players during the character creation process by advising them to select options that will serve the adventure or campaign that awaits."