Writing on the Web involves slightly different approaches than print-based authoring.  Here are a few tips.

The shorter, the better: Reading on a screen is more difficult than on paper.  Keep it short. Even when there's no copy desk to force you.

Use one topic per URL: Avoid "catch-all" pages covering a wide range of subjects.  These pages can often grow too long to be usable.  Instead try "see also" links at the end of a page/article or use contextual hyperlinking (see below).

Use an active voice: "'Do it,' don't 'will have been done' it. Reserve passive voice for situations where you don't know the subject, such as crime and court reports. But even then, try to cast as much of the action in the active voice as you can."

Use strong verbs: "The best verbs demonstrate action. If you're writing a string of weak linking verbs, think about the action that's happening in your post, then rewrite a new draft using nothing but nouns and verbs in an attempt to better engage your vocabulary."

Attribute sources: Not only does this add to your credibility, but it can provide a means of locating additional information.  Even better, if the source is the authority, just link to it instead of to maintain a copy!  See "contextual hyperlinking," below.

Use contextual hyperlinking: "Online narratives should allow readers to "branch off" and click through to other, more detailed, supporting content, depending upon a reader's level of interest. Almost all journalism refers to other sources, but online, a writer has the ability to link readers directly to those supporting sources. Note the URLs of those sources when reporting, and work those into your piece with contextual hyperlinks.

"Try to link those URLs to the relevant proper names, keywords and phrases, rather than to the URLs themselves written out, or worse, the over-used 'click here.'"

Use formatting: Break up a page using formatting

• lists 
• headers
• blockquotes

Try authoring content in plain text first (use spacing to organize content) and then use formatting (lists, bold, etc.) to provide additional emphasis of the organization.  This is especially encouraged if you author in another program, such as Microsoft Word, and then paste into CMS.

Most importantly, keep formatting consistent.  Avoid unusual/unexpected extra spacing, bolding, or other formatting.

Make it easy to read: Avoid blocks of text more than five lines long.  Try resizing your window to be sure your text is usable with smaller windows, particularly if you have a large display.

Use spell check: Click the  button in the RTE for an automatic check in CMS.  Don't forget to manually re-read "beacause no won wants to look like an idiot!"

Many ideas and above quotes from http://www.ojr.org/ojr/wiki/Writing/ 7/7/2008. (Archive available via the Wayback Machine)