Jakob Nielsen's excellent AlertBox column has some tips . Here are his key points. First, cut down your page's word count. Terse pages are easier to read than long pages. Second, use one idea per paragraph.
Visitors scanning Web pages often read only the first sentence of each paragraph.
As a result, important ideas buried inside a paragraph are often missed. Third, use bullet lists, bold text, and sub-headings to highlight key points. Journalists have followed the inverted pyramid style for years. A crowded Web page creates visual noise. There's nothing wrong with having white space on your page.