Another key item: safety tools.
I use a reference to my nation's movie &/or TV ratings for a start. Con play, I use US PG13 or R, by setting.
X-card is easy. Well, usually. I'll come back to it, tho'
Whiile full lines/veils for everone is usually not worth it, if you, as a GM have some, put them out at start of play, and be willing to add them at start if a player needs more, and to tell a player who states a line or veil that would break the adventure that it's not suitable. Refactoring adventures on the fly is beyond many people's skill.
Example of a "you shouldn't play": running alien as a store game, drop in player asked for a line at any gore or body horror; I noted that his line would render the scenario unplayable. he found a seat at an D&D AL table, instead.
The X card has two issues as it was originally defined: it doesn't provide information on what to avoid, and a small few players will abuse it. That original definition is an instant fade to black, no questions asked.
I ask for what the trigger was, so I can avoid it further. This one small change also nerfs the few abusers of it, somewhat.
Also, in con games, be attentive to onlookers complaining about content. Not everyone will play; a few are there to see how it plays, but either couldn't get a seat, or didn't want to play. If you're causing the onlookers to cringe, you may be running a scenario that's not suitable for con play due to subject matter.
The collective factor: (Not a safety tool)
Conventions axiomatically have a large attendance. You should remember that players are going to have a harder time than normal understanding you, and you them, due to the background noise.
Misperceptions in con play can result in unintended offense being taken. Practice GMing with significant background noise. Don't rely upon careful wordings.