AP (Associated Press) style is the standard format for press releases because it matches how journalists write. Following AP style increases the chances that your release will be picked up because editors do not need to reformat it.
Key AP style rules for press releases: use the inverted pyramid (most newsworthy info first), write in third person, use active voice, keep paragraphs short (2-3 sentences), spell out numbers under 10, use the Oxford comma sparingly, and always include a dateline with the city and date. The lead paragraph must answer who, what, when, where, and why in one to two sentences.
A standard press release structure includes: headline, dateline, lead paragraph, supporting quote, body paragraphs with context and details, company boilerplate (About section), and media contact information. The release traditionally ends with '###' to signal the end of the content.