To be effective as a PR writer you'll need to learn the basics of journalistic style. Unless you're a regular newspaper reader, a lot of this won't come "naturally." And you will have to unlearn some things you've been taught about writing.
In the classroom I ask students for an analysis of journalistic elements in news articles. They determine who is at the center of the story, what they are doing that is newsworthy, when and where it will take place, and why (or how) -- in what way -- is it significant enough for an editor to take notice. Those are the "5 W's" of journalism. Editors expect a story to be clear on the 5 W's. (As an online student, you should try this exercise yourself, using news articles chosen at random. )
If your client likes the story but the editor doesn't, you go nowhere. When you've gotten a sign-off on your press release, from your boss and/or your client, it's sent to an editor -- sports editor, food editor, business editor, etc., depending on how you addressed it.
If you're lucky, the editor will spend a few seconds looking it over. The first thing she'll do is notice the letterhead -- is it from someone important? -- and the format -- is it professional-looking? Then, if you're lucky, she'll read the headline -- is the subject something promising?
Then, if you're really lucky, she'll skim-read the first paragraph. If you have written that lead paragraph effectively, the editor will take an interest -- and you will have cleared the first set of hurdles.
The editor will assign it to a reporter -- "Bob," she'll say, "take a look at this and see what you can do with it." Or maybe, "Sue, give me ten inches on this story." Your press release has now been promoted to a potential story, since a reporter has been asked to use your information and come up with something that might appear in tomorrow's news pages.
"Hey!" I hear you saying. "It's already a story." Nope, it's a press release. It's potentially news, but it's not news until the news media has taken possession and made it its own.