I expect you to be on time and make most sessions. You don't have to make every session. If you miss a session, we may leave you out of the game that session or run you by "NPC rules", which means only I see your character sheet, I click skill checks and other actions, the other players tell me what you do that round.
I expect you to play a character that has a reason to cooperate and support your fellow party members. This mean no pvp, no stealing from the party, but more than that, it means your PC will help the other PCs and your PC is not hostile or even ambivalent to other PCs, after you get a chance to know them.
If it develops that one PC takes actions that provide legitimate in-character reasons for another PC to not want to travel with them, one or both of you will have to take new PCs and will need to work it out between you (I might intervene if I think it makes more sense for one PC to leave, usually the one who caused the other PC to not want to travel with them but it will depend on the circumstances).
There's no expectation to use voices. That is, if you are playing a kobold you don't need to speak with a gravelly lizard voice. You can if you want, though. I will try different inflections and pacing when speaking as an NPC, but I don't really do voices.
You are expected to roleplay your character. This generally means speaking in the first person, but it doesn't have to. It is whatever you are comfortable with. However, if you have trouble roleplaying your character, you might help try first person to help. Roleplaying your character means having it do and say things (again maybe not in 1st person) that fit the character.
With that said, I don't require players to be in character all the time. In session zero, we can talk about how in-character we want to be, but my games tend to have plenty of out of character banter including in discord.
No "it's what my character would do" allowed.
This an RPG and I do want you to roleplay your character. However, that phrase is usually used when a player is not willing to go along with what the party wants to do or is killing an NPC for no good reason or engaging in other unreasonable behavior.
This behavior is a red flag. You will get the chance to make a new character who will not do such things or you'll need to find a new table.
I expect you to be respectful to other players:
of any beliefs or personal characteristics that they have shared
of any reasonable requests (e.g., "Please call me Teegon")
of others' in-game time
of my rulings: you can make a case for a different ruling but once I make a ruling, please accept it and move on
of the premise
by being reasonably accommodating
In-game time: this means allow all players at the table to have a reasonable share of the clock-time. This means letting other players speak and avoiding interrupting but see below. It means not having a character that demands extra in-game time.
Example: you want to play a centaur. Every time we come to something a horse can't navigate, we have to spend minutes of time figuring out how to get you somewhere. This is not a good use of our time.
Example: you want to play a conrasu. This is a bizarre ancestry and in none of my campaign options will anyone know what you are. This means I either need to ignore that roleplaying angle or we need to spend time in every encounter with you explaining what you are. I do not like doing this.
Example: my character personality means I need alone time. This by itself is not an issue unless you want to do that in-game and have all the other players wait patiently while you take alone-time in a hostile place where you can expect an encounter. That is, forcing solo time that other players can't participate in, even if you manage not to get your PC killed, is not appropriate for this game.
Of the premise: this means you like the premise as described for the campaign option and you agree to support actions and behaviors in pursuit of that premise. It doesn't mean that's all that matters to you, but depending on the premise, it likely means restricting your travel to certain regions, not being hostile to certain types of creates (i.e., hating all fey in a fey centric premise, unless you and I have a way early on for you to get over that hatred).
Some cooperation on the premise is required for it to work. As a GM, one of things I expect from you is that you will explore it with me. (Again, it does not mean I am railroading you down a particular plot.)
Reasonable accommodation: we all have our touch points and pet peeves but if common behaviors tend to set you off, it can be an issue. Expectation is that people are respectful to each other, but this doesn't mean people need to feel they are walking on eggshells.
What happens if I violate this behavior: honest mistakes will get a warning, but it is possible to get kicked if it is egregious enough, especially for an intolerant screed or sexual assault.