I would teach a strip-pieced Trip Around the World.
My first class was awful; we had to hand-piece some hexagons together (thing GFG), applique them on big ovals, and then quilt it all then bind to make placemats.
I would go for fast success to get them hooked, and teach some basic skills, and then let them move on. Definitely rotary cutting skills and 1/4" sewing tricks--several, so they can pick the one that makes the most sense to them. This is what I wish my first class had been! They can bring the tops to class and have the group help layer neatly (after you teach it) then do some fast and basic machine quilting, then self-bind (where you turn the backing to the front and sew it down to finish the edge.)
In short, I needed some quick and easy success the first time while learning a few basics so I could strike out on my own.