They are also setup in a top-rich to bottom-lean format--think of an inverted pyramid with meaty intro news on top, a meaningful quote with basic attribution data. For example: "More women are wearing clothing made of organic materials than ever before," says Annie Waterman, president of FishStox, a new fashion-forward environmentally-sensitive stocking manufacturer based in Concord, New Hampshire." And interesting background data about the company or person, with contact details on the bottom (web address, phone number and e-mail address).
Do not include any overt advertising. Keep your press release simple and factual, mindful of search engine optimization (SEO) practices, using meaningful keywords in the title and body of the release wherever possible.
Best of luck with your endeavor.