The lens (focal length)
ISO (light sensitivity)
Shutter Speed (stop action/blur motion)
f/stop (aperture and depth-of-field)
Lighting (quality and direction of light, bright sun, shade, back lighting, is a flash needed, etc.)
Composition, Rule-of-Thirds , Balance, Framing
A lot of things to think about, but all important to make good photos. I hope the participants left with a better appreciation for photography and give a little more thought to each picture to to make a memorable photo rather than a quick snapshot.