Personally, I've found it useful to think of almost everything I write as a variation on "argument". Perhaps I'm also describing, defining or explaining something, but there's always a core substrate of persuading. A integral part of defining something well, for example, is to simultaneously argue for why the defined idea is interesting and useful; without that, it's all too easy to descend into abstract nonsense.
My approach isn't universally applicable—it leads to a particular writing style—but it certainly helped me in organizing my writing and organizing my thoughts. Whenever I write I'm always making a point even if I wouldn't classically think of it as a "persuasive" essay.