Try the equipment before the class arrives to be certain the phone lines, modems, networks, computers, keyboards, overhead projectors, software, etc. Remember also to check for any software plug-ins you may need during the class such as Adobe Acrobat readers, telnet software, etc. Be calm if problems arise during class. Sometimes I have cancelled a class because the web server was down. Rarely do I make the decision on my own, but rather, keep the class informed as to what is happening and allow the group to decide what is best for them.
Many instructors suggest using class assistants when teaching a hands-on class.
I want one class assistant who remains invisible until needed to solve equipment problems. I do not want a course assistant who interacts with the students during the class. When I've taught classes with assistants who were there to assist students, I found it much more difficult to keep the class focused. The small group psychology is such that the assistants need to show they are there for a reason and the students compete for the attention of the course assistants. Furthermore, having a class assistant means I do not have the opportunity to discover what is confusing or difficult for the students.