Always remember

[NotMousse]

Don't panic.

But aside from that I've found that certain things come in handy.

Different voices are always good when differentiating NPCs, even if the voices are bad at least the players can pick up the difference.

Prep is a good thing. Some can wing it well enough, but knowing where a mod (or your own scenario) goes speeds the whole process along.

Smart NPCs always kill the mage first. The rest topple so much easier after that.

Playing stupid NPCs is just as important as playing smart ones. If your NPC doesn't have the Int of Sun Tsu then don't give them his tactics.

[Dragnmoon]

If you are running a scenario at a convention, it is a good idea to run the game prior to running at the convention. It is a good way to know the scenario. Just grab some friends if you can and run it for them. They can even get Pathfinder Society scenario credit for it!