Book: (Online) Strunk, W., Elements of Style
Strunk
(Easy to read, very useful as the first writing book to read)
American Heritage® Book of English Usage
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Bartleby Reference
Book: BUGS in Writing: A Guide to Debugging Your Prose
(Also easy to read, like a manual for checking different issues)
Book: Style: Ten Lessons in Clarity and Grace
(This is not a book for easy reading, but it can be very helpful in improving writing style)
Book: The Handbook of Technical Writing, Seventh Edition
(This can be a good reference book to put on your bookshelf)
Book: Writing for Computer Science: The Art of Effective Communication
Book: The Chicago Manual of Style: TThe Essential Guide for Writers, Editors, and Publishers
Book: Mathematical Writing book by Donald E. Knuth
Book: A Few Rules from "A Handbook for Scholars"
Scholars