I think I understand your question.
Press release frequency is important because Google likes to see a steadily increasing volume of all things SEO. In other words, backlinks, forum posts, news stories. If it sees your name gradually becoming more "popular" across the web, month by month, it perceives this as a gradual increase in your web "importance" and it will gradually move you up the rankings.
Increasing ranking on Google is a slow process, so think long term how often your going to have something newsworthy or worth a press realse. Don't create press releases that aren't newsworthy, the web is full of them, and they're just a waste of space and time.
Only post news on websites with high domain ranks, make sure you use anchor text for your key search terms.
If you have stuff to say that's not newsworthy or press release worthy consider a blog.