This is from experience running many Star Fleet Battles scenarios years ago but much should be useful for RPGs.
1. Verify from the con folks when/where your table is. Do it early. Do it multiple times. More then once, our table(s) were moved or 'accidentally' dropped from the schedule due to conflicts. Have a backup plan.
1a. Expect the con to shorten your time slot, 'for reasons'. Have a backup plan.
2. Verify what/if any special benefits you are supposed to receive for running something. Get it in writing. Bring that with you.
3. Play test your scenario as many times as you can. Different groups preferably. At least once with sub-optimal group. Note how long it takes. Assume the con game will take longer.
4. Have multiple copies of all materials needed. Assume the players will show up with nothing, expecting you to provide everything, including dice, pencils, etc.
5. Avoid using original materials at the con table. Assume at least one player will have a massive drink spill in the middle of your table. At least copies can be replaced by more copying. Buying replacement originals can get expensive.
6. Have backup copies in your hotel room/vehicle. Just in case.
7. Don't plan on using the con/hotel printer to make hard copies. It will be down or cost $1/page.
8. Since you will be an active part of the RPG, have large name tents for both player and character names. Have extras and more then one marker. Also have one for yourself and one for any NPCs.
9. Pre make your characters. Have multiple choices for each player. Some players really don't want to run the healer because they were the last to show. Better to have a party of 4 thieves then two unhappy players stuck running characters they don't like. Refer to #3.
10. Start on time or as close as you can. Better to start a player short then have the game called when your time slot expires and you are being glared at by the group of Klingons waiting for you to vacate their table.
11. If the con is providing gifts/prizes/etc to players, work that out in advance. In writing. Bring that with you. Have a backup plan.
12. Have a plan just in case a miracle happens and the group finishes early. You know those extra characters you made? Or a 2nd short scenario.
13. Have a backup plan.
14. Most important. Have fun.
The names of the cons where some of the above really happened have been withheld to protect the guilty.