A press release is a mini news story that is submitted to the news media to announce your book being published.
The headline should be short and to the point. This should include the "announcement" that you are trying to make. Do not capitalize every work of the headline.
The press release body copy should be written exactly how you would like it to appear in the story. This should be written in third person. It should be started with the date and the city from which the story originated from. The first paragraph should be a two to three sentence synopsis of what the press release is about. Make it interesting and newsworthy. Make sure to use the who, what, when, where, why and how.
The entire press release should between one and two pages. You may also include a copy of your book and a general synopsis of it. An FAQ about you and the book can be included to help the media decide whether or not to interview you or give them a list of questions to be asked.
Don't forget to include your contact information.
Here are a couple of websites that will help you develop your press releases.
I agree with you on the importance of press release. For my own purpose (which is not literary information but top auction news), I find 90 % of my information in press releases. These are direct and reliable news, not reworked by magazines. I do not use magazines any more, either on the web or on paper (but I still have a look to press agencies).
Before the web, press releases and press agencies were only accessible by the press. Now everybody has access to first hand information, but very few web users are aware of that.