Usually in the first lesson, I'd cover some of the basic warmups and stretching. Next move onto a few of the blocks, punches and kicks. If things are going good, then I'd give them a SD tech.
Its important to keep in mind that while you want to give the new student a good taste of what the art is about, its important to remember not to overload them on their first day. While it appears that I'm giving them alot of material on the first day, I always stress to them to remember what they can. Even if it was only one punch, one kick and one block..at least they'd have something to work on, and over time, the rest would come.
If the new student already had a prior background, I'd still take them through the way we did our material. Yes, a punch is a punch, a kick is a kick, but methods of execution may vary. While they may seem like they're getting bored, again, I'd stress the importance of getting the basics down properly.
When it came time for the group class, I'd make sure that I put them with another student. This was not done so that the student can take over the teaching of the material, but to assist them with any basic question that they may have. Kind of like a buddy so that they don't feel like they just got thrown to the lions!!
Mike