Forbes have published a great article on effective presentations:
1. It’s About You, Not the Slides
2. Let Your PowerPoint Slides Support Your Point, Not Make It
3. Incorporate Graphics Into Your PowerPoint Presentation to Evoke Emotion
4. Keep Your PowerPoint Slides Simple
5. Tell a Story with Your Presentation
By the way, if you are creating presentations on a Mac, have you tried Keynote? It’s powerful and easy to use. I have used both and find Keynote more intuitive with very powerful features.