1. The unexpected will rivet audience attention. Breaking a pattern is a very basic way to grab attention.
2. Be careful with negative instructions. If you don’t want your audience to do something, don’t even put the idea into their heads.
3. Take words seriously. If you want the audience to take your words seriously, make your font size huge and clearly visible.

You can read more ideas from Laura Bergells at: http://maniactive.com/blog/