From Firefox developer, Ben Goodger:

It's great when people make contributions in the form of ideas and proposals, but it's even better when they're written for busy people. Here are some examples:

Making important points up front
Clear taxonomy of headings, and lots of them
Writing clearly and succinctly
No long, unbroken paragraphs or tracts of text.
Preferring bulleted lists with clear points to paragraphs.
Use of emphasis in formatting to make important things clear

...via digg