I know tech breaks down, and most frequently breaks down when you're trying something new in front of an audience. But this is exactly why I try new things in front of an audience. I know that people live almost in fear of their tech breaking down - hence this "survival guide" helping teachers cope with the inevitable problems. But while the suggestions here are very useful - I've used almost all of them myself - the most important tip is missing: solve your problem openly. While you're working on the problem, describe what you're doing, how you planned for the problem, and how you're addressing it. Let students know your thinking process. Let them see you think! I've done this in front of full auditoriums - and had people come to me after to say that this was the most interesting part of the talk.