Earlier this year I put together this summary of tips on writing for the web, at a client's request. I've found myself going back to it several times since then. Hope it helps!

Read this article by Jakob Nielsen (very well-known expert on web usability). It’s old, but still very relevant: “How Users Read on the Web.” In addition, here's my bullet-point summary of how to write for the web, combined from the Nielsen article as well as several others.

Be concise.

• Write it, then cut it in half, then cut it in half again.
• Good article from Yahoo! Style Guide on getting to the point: http://styleguide.yahoo.com/writing/write-web/get-point.

Make it scan-able.

• Use short sentences.
• Use meaningful subheadings, not “clever” ones.
• Avoid long paragraphs or large blocks of text.
• Use descriptive titles.

Use the inverted pyramid structure.

• Start with the conclusion.
• Present remaining points in order of decreasing importance.

Make it credible.

• Link (within the body of a page) to supporting and/or supplemental information.
• Outbound links (to other sites) make you more credible, both to human readers and to search engines.
• Check facts, spelling and links. http://www.qld.gov.au/web/cue/module8/p05-establish-maintain-credibility...
• Avoid “marketing-ese,” or traditional marketing language. It’s a turn-off for web readers. http://www.sun.com/980713/webwriting/wftw1.html