One way to improve your blog posts, press releases and long-form content is to read good non-fiction prose. It is a pleasure in itself. It also reveals how professional writers solve their writing problems: telling a story, choosing quotes, showing people and places etc.
Because I write for a lot of magazines, I tend to read a lot of magazines. Here are some recommendations - you won't read a badly written, badly edited article in any of them:
The New Yorker is my favourite. At its best, the writing in it is dizzyingly good. A friend of mine works at Vanity Fair, a few floors above the New Yorker in their shared Times Square offices in New York. One time, when I visited him, I got out of the lift on the New Yorker floor and did homage at the door. It's that good.
There are good books too. Anything by P.J. O'Rourke, who is a journalist first and a humourist second, is good. I like Stephen Bungay who has a DPhil* in history from Oxford, worked at Boston Consulting Group as a management consultant and then wrote two crisp, clever books about the Second World War: The Most Dangerous Enemy and Alamein. (Don't you hate when you find someone who appears to be having the life you most envy.) I'm just reading John Lewis Gaddis's The Cold War. It's very good - condensing a lifetime's scholorship into a reader-friendly general history.
* Amazingly and delightfully, Stephen Bungay read this post and emailed me. Hence the correction. His truth is more remarkable than my fiction: "However, my degree was not in history. I dropped it after O level. History as taught in school bored me, but I kept it as a hobby. My first degree was in Modern Languages and my D Phil in philosophy. Many years later the hobby took on more serious form." With two published history books to his name, I think that would count as an understatement.