You've picked the module you want to run or finished establishing your homebrew world. Your players all have characters ready to go, and you're excited. So...now what? Do you just jump into the campaign?
Well, you definitely can, but you can make your life and the lives of all of your players' lives much easier if you run a session zero to set your ground rules and get everyone in position for session one.
Here's how you can go about setting up a session zero to set yourself and your players up for success.
What is a session zero?
A session zero is a tabletop gaming term for the first time you meet up with your players about a new campaign before it starts, before the official "session one." Hence the name. Session zeroes might include all players or be held one-on-one and are largely for establishing the characters and their sheets, going over important backstory moments, and getting all of the characters in the right place at the right time to begin the adventure.
Typically a session zero is going to be significantly shorter than a full session of D&D or other roleplaying game. While full sessions might last four hours or longer, a session zero isn't liable to run longer than about two hours even if everyone is involved. This is because you're not actually playing the game yet - you're doing all of your prep work. Think of it like setting up the board before you start a boardgame, or doing the character creation and saving before you start a video game.
Why should you run a session zero?
Tabletop roleplaying games have a lot of moving parts. You've got anywhere from three to eight or more players, each with unique character builds and backstories. These players will also have different levels of experience with the game - some may need more help than others to build and start playing - and different boundaries about what they're okay with playing out and what they would rather stay out of the game. Beyond even this, every table I've ever played at has had different home rules for how mechanics are interpreted and how the game is played.
Having a session zero lets you get to know your players and their characters ahead of the game, which, as the game master, can make your life significantly easier when it comes to weaving characters and their backstories into the story you're trying to tell. It also lets you break the ice with your players; they can get to know your DMing style and the playstyle of the people around them so that they can assess whether this table is right for them. If it isn't, they can easily step down or rebuild a character without having to worry about coming up with an in-game reason for doing so and without your having to write around them.
Finally, when it comes to boundaries, session zeroes are the perfect tool for making sure that everyone feels safe and happy with the game and how it's played. These healthy boundaries can help you avoid potential fights or deeply uncomfortable situations later on. For all the complexities of TTRPGs, it's important to remember that they are still just games; it's not a game if someone gets hurt.
How to run your session zero
So how exactly do you get started with running a session zero? To begin with, you coordinate with your players about the details. They should all have this information before you meet at all:
The campaign name and description. This might mean telling them the module you're playing or the name of the homebrew campaign you've come up with. It also means offering a brief synopsis with the setting and the big hook.
The tone of the campaign. Let your players know whether it's a serious or a silly campaign (well, which one you intend it to be, anyway).
The playstyle you'll be using. Describe how you'll be playing (in person, online, with DDB or another virtual tabletop sim, etc.) and the basic skills you're expecting to come up a lot (combat, magic identification, stealth, diplomacy, etc.).
How long you expect the campaign to run. Is this a one-shot or a full-length campaign?
The character creation metrics. Will you be using standard array, rolled stats, or point buy? If it's point buy, how many points with what minimum and maximum? Will you be doing feats or ability score increases, or will you be doing both?
The rules on homebrew. What are you accepting? What are you denying? Is any homebrew allowed at all? What about Unearthed Arcana?
Any home rules your table plays by. Do you burn sheets? Do you allow NPC romance or R-rated scenes (even if they're fade-to-black)? Do you do grievous wounds? What happens on crits?
For example, here's what my Wild Beyond the Witchlight campaign looks like according to this pre-campaign breakdown.
The Wild Beyond the Witchlight. Your characters have been tasked with visiting the Witchlight Carnival to find the entrance to Prismeer, the faewild domain of Lady Zybilna, on behalf of one of her warlocks. In doing so, you'll discover the sinister fate of the realm where everything is not as it seems as soon as you step through the looking glass.
This campaign is lighthearted and funny, though it definitely has some dark elements - I like to think of it as being on the opposite end of the tone spectrum from Curse of Strahd.
The game is played live via Discord using virtual dice rollers and character sheets, though physical dice are allowed with picture or video proof. The key skills in this campaign are diplomacy and stealth, with limited combat.
We're using character creation rules established by my career DM partner for more powerful characters. Everyone starts at level 5 on a 35-point buy, with feats and ASIs and a level 1 feat for free. Yes, it's overpowered. Yes, it's very fun.
Homebrew is allowed, including UA, as long as I look over and approve it first. No guns.
No sheet burning, romance is allowed but no R-rated scenes, and we're not doing grievous wounds unless a player asks for it. On nat 20's, you roll double dice damage if appropriate - other than that, you gain some RP reward. Nat 1's consequences will depend on what you were rolling for. Neither are automatic successes or failures.
Hopefully, that gives you an idea of what the breakdown should look like.
Share this information, then give your players time to create characters. Once everyone's got a character, set up a time - either with each player individually or as a group - to have your session zero. Try to have your session zero at around the same time you expect to be playing the actual campaign.
Bring everyone together
Your session zero is your first opportunity to get everyone in your party together at the same time, in the same place (whether that's in person or virtual). This is the best possible time to compare calendars; tabletop gamers are infamous for being unable to keep a schedule, so being all together in one place long enough to discuss when you can all be available to play is a must.
As a side note, this is also a good time to discuss whether you will be allowing head crabbing, which is the act of a DM or another player taking over a player's character when their original player isn't present for whatever reason.
Get to know the characters
As I said, one of the main reasons for having a session zero is to get to know our characters and your party before you shove them all together on an adventure. Obviously, you'll want to know what everyone's races and classes are, but it's also important to understand your characters' backgrounds so that you can hook them into the story on an individual level.
One of my favorite ways to do this was introduced to me by my forever-DM partner. For one of our campaigns, he asked us to create something called a 3x5. This means you're creating a list with five categories, each with three items in it:
Allies
Events
Locations
Rivals
Enemies
These are things that are important and relevant to your character. By giving your DM this list, you're building the character out for yourself, which can help you improve roleplay, and giving the DM free NPCs and plot points to weave into the story as they see fit.
Once you have all of your player characters' background information, you should make sure that all of the characters are in the right place, and that they have a reason for meeting there - for that, you might set up a plot hook for them to explore.
Set your boundaries
The most important rule of playing D&D, beyond any mechanics or stats or rolls, is this: real life comes first. You and your players are, above anything else at all, people, and deserve to be respected as such, and that means setting boundaries in your game so that everyone can have fun.
I mentioned this briefly earlier, but let's look at those boundaries in more detail. In your session zero for a tabletop game, you should discuss:
The level of detail for gore or violence you're okay with describing or witnessing
Whether or not you're willing to allow or participate in in-game romancing and flirting between player characters or between player characters and NPCs
Whether or not you will allow or participate in sexual themes - including pregnancy - and how that will be handled
Whether there are any specific triggers or difficult subjects that should be strictly avoided in the campaign
Your table may also set up a safety system that includes a phrase or signal that will immediately pause the game so that someone can raise a concern or stop a topic before it makes them extremely uncomfortable.
I know this can be a controversial idea, but in my personal opinion, boundaries like this are vital to good gameplay. A DM or player that refuses to participate in a safety system like this is one that I will never play with under any circumstances, and a violation of my safety terms will immediately cause me to leave a game with no negotiation.
As with any other tabletop roleplaying game, Dungeons and Dragons is just that: a game. While I understand well that fiction can and should cover difficult topics, I need to consent to those difficult topics; if I am being hurt by a game, it's not fun and I don't want to play.
Conclusion
Tabletop games can be incredibly fun to play if you set them up correctly, and a session zero can go a long way toward making sure that everyone involved is on the same page in terms of expectations. Tell everyone what to expect in a good session zero, and you can expect some amazing roleplay that's more invested, entertaining, and productive.