Here are the guidelines that PRWeb, the free wire service for news releases, suggests writers follow:
Is your news "newsworthy"? The purpose of a press release is to inform the world of your news item. Do not use your press release to try and make a sale. A good press release answers all of the "w" questions (who, what, where, when and why), providing the media with useful information about your organization, product, service or event. If you read your press release and it reads like an advertisement, rewrite it.
Start strong. Your headline and first paragraph should provide the detail. You have a matter of seconds to grab your reader's attention. Do not blow it with a weak opening.
Stick to the facts. Tell the truth. Avoid fluff, embellishments and exaggerations.
Pick an angle. Try to make your press release timely. Tie your news to current events or social issues if possible. Make sure your story has a good hook.
Use active, not passive voice. Verbs in the active voice bring your press release to life.
Beware of jargon.