If you use Powerpoint, think about this:
Never read the words. Your powerpoint slides are not supposed to be a teleprompter. If you want your audience to read the precise words on your slide, stand back and wait quietly until they do. Otherwise, keep words to a strict minimum and tell them your story. If you want to talk about pollution problems in China, show a picture of a dead bird, not a slide full of statistics from the United Nations on climate change.
Slides with no words are 10 times more effective than slides with text.