An expert presenter will rehearse his presentation thoroughly—and will be sure to do so on the exact same laptop, projector, and even in the same room where he will give the talk. But the rest of us can’t always afford the time for that, which is why problems crop up. When they do, don’t lose your cool. Have a troubleshooting backup plan ready to shift into as gracefully as you can. To help develop that plan, we’ve culled a few common mishaps to keep you one step ahead of the chaos.