Writing for the Web - "Content is King"

Keep your text simple and written in plain language. Unless your audience requires technical or legalese, stay clear of "spelling bee" words.
Always remember that you're also writing for search engines, so make your words count. 200 plus words per page focused on a specific topic is a good start.
If you have the unusual case of a page being too long, you can break it up into several linked pages. Though, this is purely a personal preference and isn't necessarily preferred. Refer above to tip #2 if you need a standard.
Font sizes smaller than 10 points are hard to read. Use a font size of 10 point or larger for the body of your page. Search engines are acutely aware of the H1 tags for headings and p for text in the body of your paragraph. So use them wisely, i.e. break up your text-rich pages with HI, H2, H3 tags to maintain interest in your topic.
Use a spell checker and carefully read what you wrote. Let others read it over and check for mistakes and readability. Typos can be embarrassing.