Session 0

Session 0 is my favorite name for that special opening game session where no actual play takes place, but rather players sit about with furrowed brows, either painstakingly building their character or looking bored while waiting for others to finish. There are occasional outpourings of excitement (players gushing details from their character's "deep backstory" or the DM spouting tidbits about their "custom setting"), but on the whole it is the least engaging session of the coming campaign.

I don't aim to change that. It is, perhaps, the way it must be. But, I DO aim to make sure Session 0 isn't a waste of time, that it gives a solid foundation necessary for a successful long-term campaign. 

Here's what I do.

0) Have the Players Read the Relevant Rules

This is labeled "0)" because it is the step BEFORE Session 0.

Players need to know the basic rules of the system you're using.

Don't make them read every little submechanic, and CERTAINLY don't ask them to read up on the various character build options - but they should know how stuff like fighting and magic work.
This will, ideally, save a LOT of time you'd otherwise spend repeatedly explaining basic rules to puzzled players trying to build their characters.
Not all your players will read the rules. This is not the end of the world. Still, ASK THEM TO.
Not all your players will remember the rules they read. This is fine. Still, REMIND THEM to try looking rules up before asking you.

1) Explain the Campaign Premise

Every campaign has a premise.
Every one.
Even if it's just "yeah, you guys are a band of pseudo-medieval fantasy types who got lost in the woods and find themselves in a strange place. It's got lotsa fairies and trolls. You need to figure out how to get back to where you came from - and I doubt the trolls are feeling helpful."

So, you need to LAY OUT what the players can generally expect from the campaign - both in terms of setting (likely allies and enemies, character options, tech level) and tone (mood, flavor), since these may be important for players to account for in step 2).

OBVIOUSLY keep any mysteries or plot twists to yourself. BUT you don't want players showing up to a police drama/horror campaign set in a remote area of Alaska with a character who reads like a gay ex-SEALS Arnold Schwarzenegger.
^ That literally HAS HAPPENED to a friend of mine - while DMing his first session :(

Sometimes, the DM has ideas for MULTIPLE campaigns they'd like to run. If this is you, don't be afraid to bring those options before the players, explain their premises, and have them decide which they'd like to play!

2) Build Characters

This follows on pretty straightforwardly from 1).
DO NOT be afraid do disallow character classes or builds, whether on mechanical or tonal grounds. (I always ban druids from my campaigns, for example - for BOTH reasons.) Character classes should fit the chosen setting. It's part of the storymaking aspect of roleplaying games - a character with no place in the setting sticks out like a sore thumb, breaks immersion, and makes it difficult for the world to interact with it.
DON'T ask for a "backstory." They are 1) time-consuming to write, 2) not fun to read, 3) always forgotten about or contradicted, and 4) not desired by many players. All you and each of your players need to know about their character is WHO THEY ARE and WHAT THEY WANT. These can be very simple things. (That being said, if some screwed-up player wants to write out a "deep backstory," shrug and let them. And then read it when they're done, and try to incorporate an element or two into the campaign, because you are a kind and caring DM and they put in all that effort and care. But DON'T YOU DARE put the idea to make one in their head in the first place.)

Now - and this is THE MOST IMPORTANT PART - an aspect of what each character "wants" must tie in with the campaign premise. That is, each character must have a reason that they are part of the campaign, and that they band together as a party to rise to the challenges they face. Characters without reason to be there just end up as a drag on the campaign - the player will always have to be justify why their character is still part of the party, given that what their character wants has no connection to the goals as a party as a whole. Characters without reason to be part of the party are POISON to a successful campaign. Make sure you establish each character's reason during Session 0. Don't approve a player's character until they have such a reason.
[Edit: I actually just read The Angry GM's article on this bit. If you want a lot more detail on specificity on what to go for in getting a party together and keeping it together, check it.]
[Edit2: most of the stuff I write is more for GMs, but here's something for players: if your GM isn't doing a good job requiring characters to have a reason to be part of the party, get it together yourself and start proposing common goals or means or motivations to your fellow players. A friend and I recently had to do this for a VERY directionless campaign that basically several odd characters dicking about independently until we realized the DM had no plans to do this for us, we had to do it ourselves.]

3) Decide on Play Schedule

Doesn't have to be set in stone for the long term - but you at least need to know when your group is meeting next. This is the best time to establish that, and explore expectations for the continuing schedule for the group.

I like to run weekly games with short sessions. Some groups may do better with longer sessions, or less frequent games. See what's best for your players.

That's it.
All in all, it should take around two hours. Perhaps one, perhaps three. (It will take more like three hours if your players don't know the rules to the game system you're using, or if you're having the players choose from among multiple campaign options.)

A Few General Tips
Be friendly and welcoming. Encourage players to make connections with each other. (Might also be helpful to encourage their CHARACTERS to be built with connections, too.)
Provide snacks, or delegate the task of bringing snacks to a player or two, even if it won't be a customary fixture of following sessions. Snacks alleviate boredom, which is something that Session 0 is especially vulnerable to.
Keep the group spatially together. Not necessarily at the same table, but definitely in the same room. (I like a room with couches more than a room with tables for Session 0, but this is just a personal preference thing, haha.)
Feel free to experiment with the ambiance by altering lighting or playing music, but it's probably just BS tomfoolery to do so. (But hey, a certain kind of player digs that effort.)

Go start that campaign.


(Reader: what does your Session 0 look like?)