I like DC's point about starting off with an introduction to Leather types, weights, uses etc. Speaking for myself when I first started out that would of been invaluable. It took me quite a while and more than a few wasted purchases to get my head round all that.
I was always taught when planning a lecture in the Military to "tell them what you're going to tell them, then tell them and finally, tell them what you've told them". A hand out or two might also be a good idea, that way they don't need to be taking notes at any point
during the lesson and, if they take a few of your lessons, they get a small collection of your notes they can use for reference.
I have always found that the process of putting a lesson plan or lecture together, even for subjects you think you know well, ended up with me having a much better understanding of the subject in hand. Mainly due to the need to make everything correct, you end up working
out answers to bits you hadn't really thought about before and the whole thing becomes clearer in your own head.
Good luck with the lessons and I'm sure you'll get as much out of giving them as the potential students will get out of attending.