Naturalness. Believable. Can't know you're reading! And read must time to visuals. This skill is invaluable. Be sure you know how. It's the most popular field in voice work today! Training films, TV shows, everything uses narrators and you've got to be able to do this. Tips: Read scripts into IPHONE or some device you can play back. And vary your times. Faster, slower, and don't be uniform. Ebb and flow as in conversation. Practice. Then, get with a coach who can help.
Bettye Zoller Seitz