When the media publicize your product or service at no cost to you, they are practicing journalism, not advertising. So, your release gets trashed if you leave in any clues of being insensitive to the difference.
The most telltale difference between journalism and advertising is that grammatically, ads address themselves directly to the reader while journalism usually employs third-person writing. Try to avoid the word "you" or "your" in the headline or main text of a release.
Instead of "Now you can shop for worms without leaving home," for example, write, "Now fishing enthusiasts can shop for worms without leaving home." In place of "Call 888-777- 7788 for the store nearest you," write, "Interested parties can call 888-777-7788 for further information."
Avoid the rushed, over-enthusiastic tone of an infomercial. In print, this means staying away from exclamation marks and from any self-praise that is not factual. Attribute any subjective comments, accolades or predictions about the success of your offering to named individuals within quotation marks -- preferably to third parties not connected with your company, like customers or industry experts. (Of course, you need those third parties' permission to do this.)
For instance, "A Garage-for-You franchise offers an ideal way for handy men and women to earn an impressive income in their spare time" represents an unsupported opinion. You can fix it by explaining what makes it ideal, as in, "Because of its low buy-in fee and easy-to-follow marketing methods, a Garage-for-You franchise..." Or, you can fix it by saying who says the franchise is ideal -- a satisfied franchisee, named and located, or some sort of uninvolved business leader.
You'll be tempted to toss in everything that makes you mediaworthy. Don't. Make sure you have one central point in each release and that you include only the background and commentary that supports that point. Diffuse copy gets confusing, and dilutes the impact of your primary message.
If someone can read your release and respond, "Yes, but what IS it?" you have failed. I have seen press releases for new products that I could not visualize from the verbiage, or for services that I didn't have a clue how they would work. You're always better off including too many details about your offering than too few. If in doubt, have someone unfamiliar with your product or service read the release and ask them to describe what you trying to publicize.
The key word to remember is "detail." Instead of "Jackson's new book contains information designed to benefit any stock market investor," write, "Jackson's new book contains seven principles of market analysis that enable even casual investors to choose profitable stocks." Even better, describe two of the seven principles right in the release.