Two pieces of advice:
- Make every character and place show something specific to the setting.
- Make one special character or place prominent through the whole session.
Everything is [This World]-ish
You don't have a lot of time, so you want to show what makes the setting interesting and unique. If religious orders are very prominent in the world, have the party stay at a monastic-run house for travellers, rather than an inn. If death magic is significant in the story, toss in an encounter with some walking undead instead of orcs or goblins. If the setting is Roman-themed, have an local clerk for the imperial administration give the party information, rather than a bartender.
The truth is that players tend to ignore dense chunks of information thrown at them. If you give them handouts with paragraphs of text, they probably won't get read.
One Important [This World]-ish Thing
Pick one character or place in the plot of this story. It could be the villain of the plot, or it could be the location the party is spending its time, or it could be an ally or patron of theirs.
Make that One Thing very grounded in the feel of the story. If the players have forgotten everything else that happened in the game session a year from now, they'll still remember the One Thing.
Let's say you're running a game with necromancy and a Central Asian feel. The villain could be some khan's personal soothsayer, a shaman who dances and drums his way around the fire to raise the skeletal remains of fallen warriors. The party meets him when they're first introduced to the khan, and the shaman goes into a trance and pronounces a curse on them. They hear the sound of his drumming in their dreams as they sleep out under the stars. They fight his skeletal warriors who whisper one word over and over again in the shaman's voice. That villain, the game's One Thing, shows up again and again to reinforce the idea of the setting.
Followup
Tell us about the setting/plot/world/characters, if you can, and I'm sure we can come up with some great ideas for how to apply these concepts to your plot.
I do several things to keep the player characters interested and invested in each other.
- At the start of the game, I insist that players coordinate backgrounds (subject to my approval) such that each character know at least one, and preferably two or more, of the other characters. In general, I prefer these connections be positive; the most negative I will usually tolerate is on the order of a friendly rivalry. In general, I also prefer that if you start from any one character, you can get to any other character by following these pre-arranged links. (In graph theory language, the players are all connected, although indirect connections are fine; the alternative would be two more more sub-groups connected internally but not to each other.) And finally, I try to ensure that each connection is more than trivial, but not necessarily life-binding.
So for instance, "We met in a bar twenty years ago and never saw each other again," is trivial. "We are cousins who are best friends and we are rarely separated," is life-binding and more than I look for (although it's fine if that's what they want.) Things like the following are what I look for, and/or what I've seen in the past:
- Our characters served in the same unit years ago, and knew each other, but haven't kept in contact...
- I served as a mercenary escort once, while he was travelling with his master from here to there; along the way, this happened....
- We weathered the siege/plague/earthquake of wherever together some time back....
Now, some players are genuinely not wired that way-- if you ask them for backstory, they freeze; if you given the one, they can't connect to it. When I run into a player like that, I have to respect that, but I try very hard to get everyone to adhere to the guidelines.
That does not directly solve the problem. (It actually solves the problem of getting the characters all on the same page at the start of the game.) But it does often give me enough to work with to do the following:
- With enough insight into character backgrounds, and with overlapping backgrounds, I try to give every character an mid-term to long-term goal or plot arc, and then I try to modulate that by giving at least one other character a minor to moderate interest in how the first character's arc plays out.
It's important (to me, for the games I want to run) that these arcs not be strictly opposing: If one character has sworn blood-vengeance on an NPC, I won't give another character the goal of keeping that NPC alive. But I might give another character the goal of getting something from that NPC before his death, or getting the NPC to do something, etc.
And I also try to modulate this in another direction by giving other characters-- ideally, not the same one-- influence over the plot lines. So continuing that thought:
- Player A has sworn to kill Sir Odious, his parents' killer
- Sir Odious has information that will help Player B in her quest to do something else
- Player C knows someone who can be bribed into giving up information about where Sir Odious will be
In that way, for each of the various player sub-quests going on, at least one or two others will be involved somehow, even if only at the periphery. Ideally, Player B has some motivation for something to happen, and Player C has something he needs-- something at least moderately costly or risky. They are invested.
One thing I would not do-- at least not again-- is what you tried:
I've had players create characters (with backgrounds) completely secretly from each other with the hopes of allowing the character interaction to be heavily role-played at the table. Didn't work because of very incompatible characters.
I've never done that, specifically, but I've inadvertently done similar things and it never worked well. It seems like it should work, especially if you pattern it similar to what I've outlined above, but there's a structural weakness to it: If the players, starting out with the relative blindness of only knowing their little part of the background, they just might not see those connections you built in for them, and won't give themselves the incentive to start sharing information. And if your players were the sort that would do that naturally, you wouldn't have to go through these acrobatics in the first place.
Best Answer
A good place to start is this question and its answers, even though, somewhat surprisingly, "How to do this," is not explicitly called out as a question. This will still give you a good cross-section of opinion on what the thing is that you're being asked to do.
I can share my personal experiences of how I run a Session 0, though, as well as address your specific concern about player knowledge and optimization.
What I do is going to sound very simplistic: I get all the players together, ideally in the same environment (or one of the environments) that we're going to use to actually play. Right now that means someone's home with a nice big table to gather around. Back in the day, it meant the gaming shop where we could use a table, or a student center area when I was in college.
Then I describe in very high level terms the kind of game I am interested in running, and ask if the players are interested in that kind of game. This often starts out as something similar to a discussion of genre:
You can see this moves from the very general to more and more specific. It can also cover things like the tone of the game (Is player-vs-player a given? Is it taboo? How dark is this setting going to be?) and so forth.
It's really not a part of the game directly, it is a conversation, it is social preparation for the game, to make sure everyone is interested in the game and everyone comes prepared for the game that you're actually going to run. I cannot give you hard rules on how to resolve conflicts during a session 0, though, except a vague sense that since the GM is doing more work than anyone else he probably ought to get more concessions than anyone else. Other than that, this is social negotiation not unlike deciding on sushi vs pizza: It is highly dependent on the people involved.
As far as too much player knowledge goes, in my experience this is mostly a non-issue.
First, the point of the session 0 is not "tell the players what happens," but more along the lines of "tell the players what to expect." The precise genre of game you're running isn't (or shouldn't, in my opinion) be considered a spoiler.
Second, character-optimizing players will always exist, but this is fine. There are other ways to shut down optimizing players, and in the last recourse, you as GM are the one setting the challenge level of the campaign.
Consider another extended example: Imagine you have told your players you are going to run a 5e D&D game. Your unannounced concept for the game involves a background of goblin, hobgoblin and bugbear tribes unifying under the rule of Maglubiyet's priests, gathering other humanoid armies and eventually invading the "civilized" lands. In short, a very military, martial kind of a game with a lesser focus on enemy clerics.
If you keep this concept to yourself, you run a real risk of getting players designing characters with concepts and skills that are superfluous-- social movers, squishy sneak thieves, etc.
If you announce this, you're more likely to get a ranger who is, yes, in some sense optimized against goblin-kind. But that character also thematically fits the game, and may have backstory that explains why he is optimized against goblins. Or, alternately, if you have a player who is really set on being a social manipulator, you may at your discretion be able to insert some story lines and scenarios into the game which make that player shine.
Put another way, I'd much rather have a character optimized for my game and who fits well into the background, than to have a character optimized for situations that will only rarely occur. The second character is useless, and since optimizers gonna optimize, I prefer to co-opt them from the start.
(But note, even here you don't have to give away your entire campaign idea. You can keep it as simple as, "Lots of fighting with an initial focus on humanoid monsters.")