I have always found that humor is an important factor in any classroom. While I always keep things focused on te task at hand, I like to inject humor whenever possible. Students tend to feel more at ease, and I find that they often remember much more of the material presented. Sometimes I tell funny anecdotes related to the material, or I poke fun at myself when I accidentally make a mistake. Whatever the method, it is the fastest way I have found to grab their attention, and keep it. Here is a great article related to this subject:
http://www.nea.org/tools/52165.htm
