Simple lines, bars and boxes can be used to make a very powerful design. It detracts from your message if your audience thinks that you have a bargain-basement operation. If possible get your piece printed rather than photocopied. Usually, if one additional client comes because of this, it's worth it. It looks so much better, and it communicates that you are serious about what you do.
Reversed designs are harder to read than positive images.
Italic and bold faces are harder to read but good for emphasis. Use them sparingly. Thick fonts are good for headlines, but again, use simpler fonts for parts that require sustained reading. Don't be afraid to make the headline really big. 9-point text is what most books are printed in.