Do you have any idea of the needs of your guild? Are they mostly experienced quilters or a mix of newbies and experienced. Can you guage what might interest them from past show and tells?
I think how to paper piece would be good for beginners
Advanced you could offer how to do a mariners compass using either traditional or freezer paper piecing
Do you have a really good longarmer or quilter in your guild? Or can you bring in an outside teacher? Maybe a seminar on "how the heck do I quilt this" with participants bringing in flimsies the teacher could use as demo.
How to properly measure for borders
Tricks for getting points to match, such as elmers school glue or basting at the intersections and checking before stitching the whole line, double pinning (which is what I do) etc.