Where to start? I think the most important question to ask those interested is "have they ever sewn before". A lot will depend on the class's basic level of skill. I would make the first class show and tell of some of your work and then maybe a quilt in progress showing the various steps. As a handquilter I always made up pillowsize quilt sandwhiches with a simple line quilting motif. I then let them try their hand at handquilting. It isn't a quilt until it is quilted.
In group quilting the work is generally done by handquilting on a frame. It is the only way a group of people can make a "group" quilt.
If they are truly intersted then you can start with something as simple as a 4 patch using a wonderful print and a solid. It is a quick way to produce an attractive quilt with a minimum of cutting and piecing. In our instant world simplicity speeds up the process. When and if they master that you can move on to something more challenging.
My church is currently celebrating it's 250th year of existance. We are creating an anniversary quilt. It will consist of paperpieced houses with hopefully a picture of each family in the congregation in the window of the house. I am embroidering the name of the family members on a white strip at the bottom of the house. The center of the quilt will be a large square with an embroidered line drawing of the building. We hope to machine embroider some Lutheran religious symbols like the Luther Rose in cornerstones of one of the borders. It is still a question of how and whom will do the actual quilting. We are having a paperpiecing workshop for those who are willing to assemble the house blocks.