Who are your players?In a campaign game, you are likely to be playing with your friends, or at least people who you can get to know over the course of the campaign. This means you know their idiosyncrasies, their desires and their (IC and OOC) buttons. You can plan for your 10 o’clock monster to turn up at 9:30 cause you know one of your players is ill and won’t last the whole night.
In short, you can tweak the game towards what your players want. There is a sometimes conscious, sometimes unconscious discussion between the players and the GM about the shape of the campaign, where the fun is and what areas should be avoided.
In a con game, this is far less likely. You have a set piece, a prepared piece of fun for a random bunch of players. There is the possibility that when a group of players walk into the room, you will know them and be able to tweak should it be required. But on the whole, you have to be responsive to the players on the fly, judging moments and juggling plots and hoping that you are reading these comparative strangers correctly.
How will they behave?One campaign GM I know counts players in terms of their involvement with the game. Some wallflowers only count as .5, while other players are actually 1.5 in terms of their needs in interacting with the GM. The GM then fills the game with five ‘players’ regardless of how many people this ends up being.
I have great difficulty in reading one player I know - whether they are currently enjoying themselves, or not. Theirs is a stoic visage in the face of both happiness and discomfort, which frankly I don’t find reassuring to GM. I have watched them finish my games (more then one of my games) sure that they didn’t enjoy themselves. But this player keeps signing up for my games. Which I read as either they’re a glutton for punishment, or that they do actually like my stories and GMing.
In con games, the game fills up with 5 people. This may or may not end up being five players as my friend defines them. Five wallflowers will make for a hard game to GM should there be a call for interaction or movement between players. A tactical game without any tacticians in the game is likewise tricky.
How many players will come?In some ways, here is a similarity between a campaign and a con game. In campaigns, people get busy or ill. In cons, a group may lose a member for the same reason, or partial teams were unable to fill a session completely. The result is the same. You can write a game for five players, but there’s always a bit of uncertainty how many you will actually run for.
Do they know each other?The short answer is maybe. Maybe you’ll get a team of players who are friends, trust each other and are ready and willing to bounce off each other – either by roleplaying to the hilt (arguing, setting each other up for gags or what have you), by falling into the various roles required within a team to solve the puzzles you have written for them and so on.
But maybe you’ll get a group of people who don’t know each other. And sometimes that’s ok. The might be a willingness to throw themselves into the game in the same way a tight team will (a willingness to trust strangers?). But sometimes they’re not. And then you have a group of people who are not getting into the game, not seeing the fun they could have.
How to account for these variables?I think there a couple of different ways to account for it – being clear on what your game offers in the blurb, including variable game planning (a good chase scene when you need one, should you need one), good GM skills (reading people and balancing plot and interactions) and a quick discussion beforehand to talk about what players want.
Once we've worked our way though a few more of these, we can talk about how best to manage them - some of the strategies are similar I think.