Pick one you find interesting, one you are familiar with (or become familiar with it), pretty much the Cleric Cabin advice.
For example I played Walking Dead Universe at the Con last year, liked it and so decided to run it a Con this year. I got inspired by children's book I saw and decided to write a Rivers of London scenario about it. Neither game I had run before deciding I was going to run then at a convention, however RoL is "Basic RPG" and something I am familiar with.
and prepare an adventure to run a scenario during an event slot at a convention with tabletop RPGs as an offering? What tricks do you use to prepare the game, run the game, and manage the table?
inspiration -
Run a Con Game the Cleric Cabin Way
Playtest it with your local group beforehand. I've got two local groups I play with I got the chance to run the Walking Dead scenario with both, but unfortunately didn't get a chance to run the Rivers of London one, and there was a clear difference in my skill at pacing and handling the table between them. So the more you can run scenario the more familiar with it you will become.
I like to work out a timeline of what point I should be at after each say 30 minutes so I know if I need to pick up the pace or slow it down.
Always start with introductions, asking how much RPG experience players have in general, and with the system we are about to play specifically. Hand out pregenerated characters, or explain how we create characters if it is something like Kingdom or a PbtA game with playbooks. If I make pregens they will always have a bit of a backstory, a bit about any of the other characters they might know and how they feel towards them. Generally I build in some interparty conflicts and relationships to encourage roleplay between the players.
I don't play with "safety tools", but do put content warnings on the sign-up sheet and remind people about them at the start, if appropriate and ask if anyone needs to stop (or leave) for any reason they are welcome to do so. I generally play 12A or at worse 15+ games anything particularly gross or lewd we fade to black, but I gauge my audience so if I have younger kids that want to play Call of Cthulhu, it won't be as gory as if it is all adults. I tend to go to one convention that I've been going to for years, and while it has "safety officers" I don't think they have needed to do anything in nearly a decade (there was that one time with a prop sword/gun and the police being called, UK based if that matters).
Most con scenarios start "in media res" I have some sort of engaging scene to draw the players in and make them work together, I won't start in a tavern, unless it is already on fire and under attack by orc raiders for example. Most of the scenarios I run I know what things are going to happen, how the villian will drive the piece if left alone, where the clues lead, etc. But it is still worth being able to improvise as no two groups handle things the same way, the better you know your source material the easier that is (hence playtesting).
Try to make sure everyone is involved (not necessarily all at the same time) keep moving the spotlight round the table, don't let it ligger too long on anyone player. If you find one or two players are involved in a particularly long scene, leave them on a mini-cliffhanger within that scene and ask what others are doing in the meantime.
Don't worry about splitting the party particularly in an investigation type scenario, you can get more done, but keep switching between the groups to keep everyone involved.
Most slots I run in are 4 hours long, I usually have a 5 minute+ bathroom/bar break in the middle. The convention I run at has individual rooms for the games so noise levels (ours or other tables) and onlookers are never a problem.
I try and aim to wrap up about 15 mins before the slot is due to end so players can ask question about the system, say what they liked or didn't like, etc. I print enough copies of character sheets that if they want to they can keep it.
