What are some guidelines for creating overhead visuals that are easier for students to see?

DO-IT Factsheet #41
http://www.washington.edu/doit/Stem/articles?41

Following the basic design guidelines listed below can help you create overhead visuals that are easily read by people of many different ages and abilities to read and see. Large print and well-organized visual aids are particularly helpful for some students with disabilities that affect their sight, learning, or hearing.