And never use reversed type in print. White type on dark backgrounds works for projected images but is almost impossible to read on printed materials. When speaking of groups over 20, use a microphone and speakers. Put the speakers in the back of the room to reinforce your voice for those who are farthest away. We all lose our ability to differentiate sounds as we mature.
Many older people are hard of hearing.
Speak slowly and concisely. Clearly articulate each point and then pause to let it sink in. Look at your listener s faces to see if you are communicating effectively. Ask if they have questions. Once they are clear, move on to the next point.