In my courses, especially the lower division ones, I try to avoid showing complex diagrams and figures, in favor of simplified versions I can sketch them on the board, so they can draw along with me. I believe this helps impress the information being conveyed by the figure more effectively and powerfully, (1) by eliminating distracting and unnecessary detail (via simplification) that can impede understanding; (2) by providing a graphic that can serve as a reminder of the concept being learned; (3) by actively involving the student's hands and mind in the learning experience; and (4) by forcing me to slow down, to focus only on material that advances understanding of the topic.
The specific example will likely involve sketching a simplified version of the atmospheric absorption diagram that demonstrates the greenhouse effect. This figure commonly appears in introductory texts, in its full published version is replete with unnecessary detail, but functions effectively as a summary vehicle that can help students convey their understanding of the selective absorption concept.
I will need a chalkboard, whiteboard, overhead projector or some other writing surface.