Present one point per slide , with as few words and lines as possible. And use lots of slides. Nothing is more boring than talking for 10 minutes to a single slide. Use type and ornaments to guide the reader through your message. Boldface works better than italics for this.
Color helps to add interest to a slide and attract attention to the key word or phrase.
Slides and overheads are like billboards. They should be designed to make an impact quickly, and then it's on to the next one. Avoid long blocks of text each slide or overhead should be a hint, not the whole story. Whatever you do, it needs to be inviting. Make your audience want to see more of what you're presenting.