1. Keep it short
Slides loaded with text are counterproductive: they show that either you haven't understood the core point of your own work, or that you feel it to be of little use that it needs a lots of justification.
2. Keep it shorter
I was once told that "the audience already knows that you can read". Do not place in the slide text that you are going to read out loud. Rainbacon already pointed this out. I'll add that it detracts from the opinion that the audience will have of you: reading text out loud make you sound insecure, unprepared, or, perhaps worse, make them feel that you are trying to lecture them.
3. Facts
A slide is basically an image. Use it to display information that would require a very long verbal description. For instance: facts, maps, numbers, a graph, a picture of your product, a comparison of two images, a very short video of your result, etc... Use the slide to tell salient facts to your audience; use your voice to guide them to the conclusions you want them to draw.
4. Afterall, if you could just write down a paragraph instead of giving a talk...
...then you'd be better off sending an email and let them read it when they want, at their leisurely pace.
This advice comes from personal experience of two decades of presentations for academic, corporate and governmental audiences.
