The job of a press release is to suggest a story idea to an editor, reporter, writer, or broadcaster. It's a bit like fishing. Whether or not the editor takes your bait depends a lot of what kind of day they're having.
In the end, it is entirely up to the editor as to whether they use your story.
Slow news days are good times to get an editor's attention. You will do better if the editor receives your story before 3pm. Late afternoon is deadline "crunch" time for newspapers, past the prime news times of radio, and getting into last minute preparation time for TV news.
Linking your story idea to a popular story in the news can also get an editor's attention. Media folks figure the audience can only stay interested in a few topics at a time.
Finally, it's a good idea to make your release sound newsy in the beginning, saving the blatant commercial stuff for the end of the release.
