• Ten slides. Ten is the optimal number of slides in a PowerPoint presentation because a normal human being cannot comprehend more than ten concepts in a meeting
• Twenty minutes. You should aim to present your ten slides in 20 minutes. Twenty minutes ensures your audience feels engaged, that you can show you know your material, and that you can dive deeper on any of the points they don’t understand.
• Thirty-point font. When you have small fonts on a slide, and the audience notices you are simply reading the content on the slides, they will immediately start reading themselves.
Source: Guy Kawasaki