They have color transparencies, clip art, and scanners available. Use cartoons for humor. If necessary, enlarge the image or reset the caption. Use graphics to add visual excitment and interest. CIL has various clip art sources.
Readability is enhanced.
Use 36 or 48 point fonts. Never move a hot overhead projector. Bulb filaments are fragile. Overlay transparancies to show successive processes. Reveal each layer as needed.