If you're using text, choose your typeface carefully. Favour sans-serif fonts, such as Arial, as these are easier to read from a distance. You should also be generous with line spacing. Check for spelling mistakes. And then again.
Body language is very important.
Keep as much of your body in view as possible. Use separate lighting on yourself, if possible, and always face your audience. This is easily achieved by using a display in front of you as a reference, rather than turning to the projection behind you. If you can, stand to the audience's left of the screen. People read from left to right, so it's easier to look from you to the text and back again if you're standing at the beginning of the sentence.