Style

• Be concise and direct
• When breaking up text for hypertext, make the breaks meaningful, not random
• Use journalistic style - begin with a short summary, then offer details from there

Layout

• Keep pages short ...
• so people don't have to scroll
• so people can more easily digest your text
• unless you plan for the page to be printed out
• Use meaningful headers
• Emphasize meaningful points and sections (but within the bounds of typography!)

Content

• Write with less text - perhaps 50% less, according to Jakob Nielsen
• Credit your sources!
• Point out mistakes in a positive manner, with clear instructions for how to fix the problem and move on

Most importantly

• ... know your audience and know your purpose.