First and foremost, your slides should play a supporting role and not steal the show from your presentation, the story you are trying to tell, or the message you are trying to convey.
Here are some more tips:
1. Limit the number of words on each slide. Present. Don't read.
2. Stick to key points.
3. Choose an easy to read font and make sure it's big enough to be read from a distance (30pt. font or higher).
4. Change data into charts or graphs.
5. Don't add animations. They are distractions.
6. Follow the tips on the previous page about public speaking.