I feel that a Session 0 should cover a lot of these rules, they should be not "unwritten rules". They should be discussed up front prior to starting the game.

I feel that a Session 0 should cover a lot of these rules, they should be not "unwritten rules". They should be discussed up front prior to starting the game. On top of that the DM needs to find out if there are any topics that the players don't want to encounter. For example rape is a big no on my table, slavery they don't care about encountering, it gives them people to free usually. In another table even with me as DM it can be the opposite. As a side note, having a DM credo to share with players is always a good starting point. It's a list of expectations for your own conduct.