Excellent advice from Guy from 2005 that is wroth repeating. Do yourself a favor and read the entire post. You will thank him and your audience will thank him!

I am evangelizing the 10/20/30 Rule of PowerPoint. It’s quite simple: a PowerPoint presentation should have ten slides, last no more than twenty minutes, and contain no font smaller than thirty points. While I’m in the venture capital business, this rule is applicable for any presentation to reach agreement: for example, raising capital, making a sale, forming a partnership, etc.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

via How to Change the World: The 10/20/30 Rule of PowerPoint.