Expand your vocabulary. A large vocabulary makes reading easier.
Practice in front of a mirror. Read a news story, then put it down and see how much you can remember in case the teleprompter breaks or goes too fast. This step will help you in any sort of presentation, not just when using a teleprompter.
Speak slowly, clearly and using a natural rhythm. If you speak too swiftly or in a stilted manner it will be obvious that you are reading directly from a teleprompter.
Research the information you'll have to cover beforehand. This way you will be more relaxed, natural, and better able to improvise if a problem occurs.
Do not squint or strain to see the words.
Summarize what you already know or remember if the words disappear before you can read them. A good teleprompter operator will adjust the speed to match you so you can catch up.