There are three rules for writing the novel. Unfortunately, no one knows what they are. (W. Somerset Maugham)

Everyone has to develop their own writing style, based on their own strengths and weaknesses, on the subject matter, on the target audience, and sometimes on the target medium. Nevertheless, I do have some general advice on these topics:

I should point out, of course, that my own writing style is not perfect, and I myself don’t always adhere to the above rules, often to my own detriment. If some of these suggestions seem too unsuitable for your particular paper, use common sense.

Some further advice on mathematical exposition: