There is an art to good content writing that works for all aspects of an Internet website.  First, it must compel the reader (customer) to buy your products.  Second, it must contain information that the reader finds valuable and will either bookmark (place in favorites) or link to.  Relevant links to your site will boost it's ranking in the search engines.  Third, it will improve your ranking in the search engines who are increasingly becoming more content based.  If you accomplish all of these things, your chances of success are vastly improved.

As important as content is and will become don't dismiss the other search engine optimization (SEO) techniques available.  It is still critical to code your pages appropriately with meta-tags, title tags, comment tags, header tags, and alt tags (for images).  The right keyword phrases are important to ranking.  You must find phrases that aren't so competitive so you can have a chance of being found.  A website is no different than traditional off-line businesses, you must find your niche'. 

Good content writing will emphasize your keywords while still maintaining a "one-to-one" conversation tone.  This means your writing should resemble a conversation you are having with a good friend of yours.  Unless you're building a website about research tailored to a specific profession, you aren't going to write at a college level.

Good content includes:

• Identifies your unique selling position - what makes it different from the competition.
• Enough evidence to support your claims
• Highlighting benefits instead of features
• Answers the question:  Why should I buy?  It justifies the purchase to the buyer.
• Offers a guarantee
• Demands the money
• Sets a deadline or sense of urgency to act NOW.

Formatting

• Eliminate scrolling from left to right to see the page.
• Use normal 1" margins on page.
• Use at least 10 point font size, preferably 12 or higher.
• Avoid overuse of graphics which slow your pages from loading.

Language
Websites are generally seeking to see something and should follow certain guidelines when writing.  They should consistently make use of the word "you" to personally engage the reader.  The ideas must be clear and specific, sentences concise, and it has to have emotional appeal (based on your buyer profile).