Today, the wife and I are going to some friends who live up on Big Bear and teaching them how to play DnD. I've done this lots, so I just go over the basic principles behind DnD, go over the main attributes of character creation, show a friendly encounter, and then go through a small battle. That usually takes a few hours. I've rarely had someone who didn't then want to create a character and get into a campaign. Of course, my life is chaotic and I'm reluctant to start something and not be able to follow through in the long run. I'll just show them the basics and then maybe get them started for a while and then they can create a campaign of their own or continue with my basic story.