1) Avoid jargon.
2) Include the primary theme of a paragraph, and the scope of what it covers, in the first sentence of each paragraph (i.e. frontload paragraphs).
3) Use verbs in the active voice.
4) A sentence should not contain more than 20 words. A paragraph should not contain more than six sentences.
5) Make action sequences clear (e.g. list instructions in chronological order).
Those five guidelines would vastly improve many a web page content.
From the National Cancer Institute: http://www.webpagecontent.com/arc_archive/156/5/