A similar guide, aimed at people writing research papers, is “How to Write Mathematics” by Paul Halmos (1970) [1].
They both start from a similar assumption:
Lee: “When you write a paper in a math class, your goal will be to communicate mathematical reasoning and ideas clearly to another person. The writing done in a math class is very similar to the writing done for other classes. You are probably already used to writing papers in other subjects like psychology, history, and literature. You can follow many of the same guidelines in a mathematics paper as you would in a paper written about these other subjects.”
Halmos: “The basic problem in writing mathematics is the same as in writing biology, writing a novel, or writing directions for assembling a harpsichord: the problem is to communicate an idea.”
[1] https://www.mathematik.uni-marburg.de/~agricola/material/hal...