Have a plan of what you are going to talk about, and try to interrelate the topics to try to get a unified point across. The average human can retain 7 ideas plus or minus two. Keep this in mind and only use a few animals with 5 interrelating facts. For example, adaptations that make a lizard a lizard, or a snake a snake.
Go to your local nature center when it opens and talk the naturalist about interpretation. (The art of environmental education is called nature interpretation, it was part of my degree in recreation and wildlife management)
Doing reptile education is great, but go with an educational purpose. A badly planned program has the potential to do more harm then good.
For more information look into the national association for interpretation.