Narrow down your topic. Don't clutter the voice over with superfluous details. If the topic is on the local chili festival, don't give any more information than the viewer needs. Just give the five "W's": Who, What, Where, Why and How.
Leave plenty of space in the margins and make sure to double space the text. The person reading the copy may need to make notes or instructions on the page.
Use 12-point font and do not put anything in italics. Only write on one side of each page and don't staple pages together; use a paperclip. If you staple your pages, they will make noise when turned, and the microphone will pick up the noise.
Label each section of the copy clearly, making the transition from topic to topic easy to see and understand. Be sure to include page numbers, as well.
Begin and end each section on one page, if at all possible. This will minimize the reader's confusion when transitioning from section to section.
Spell the words phonetically if the words are unfamiliar to the reader. Also, always write out numbers, such as "eight," and not "8."
Write simply. Don't use large complicated words just to sound smart. Always remember your audience. You're writing the voice over for a large news audience.
Read it out loud. Have others listen to it. Make sure the voice over flows and is not awkward sounding.
Proofread your copy and have somebody else proofread it, as well. If you must, rewrite it until you have an acceptable piece of copy.