This is probably the cleanest Intro to writing in 'classic style' that's out there.
The idea is that when you write, you imagine a scene of 'joint attention' -- where the reader is an equal to you, and 'sees' what you 'see' (even if this is abstract or linguistic); your job is to point out elements of interest and pass on context, motivations and observed details which your partner may not otherwise have noticed, or may not perhaps mark the significance of, in the expectation that they will understand and agree, but without the presumption of anything that's necessary for what you want to point out.
That's to say that classic style isn't patronising, but is explicit; it isn't ostentatiously technical and academic, but it is accurate; it isn't just stating the obvious, but it is thorough; it isn't handwaving and casual, but it is concise.
These qualities make it a good style for essays and exams. Caveats: in an exam, you should think with your pen, rather than plan silently in your head and then attempt to commit a perfect performance to paper of only the conclusions you're certain about. Tentative alternative readings are welcome and gain marks -- this is exploration and evaluation at work. Classic style aims for a polished and confident statement of the simple truth; and in English, often ambiguity is inescapable, and polishing is a task for coursework.
http://blog.press.princeton.edu/2011/06/24/op-ed-by-the-authors-of-clear-and-simple-as-the-truth/
