Not a source, but rather an exercise: give yourself a tight word count and rework your essay until it fits. When one third of your article has to go, you start looking really deep into how to extract as much value as possible out of every word.

Google has a few courses about technical writing for engineers:

https://developers.google.com/tech-writing

Death Sentence - The Decay of Public Language, by Don Watson.

Blisteringly good. Not aimed at technical writers, but encourages you to think about how to really use language effectively and robustly.

There are innumerable sources online for improving technical writing and they all generally repeat the same conventions and "rules". I tend to warn people, though, that over fixating on technical writing will not make you a great writer but just a capable technical writer.

If you're looking to improve your writing in general, then I think Joseph Williams' "Style: Towards Clarity and Grace" is the single best book on the subject written so far. Rather than simply state certain "rules", it methodically workshops examples to show how you can write and rewrite a sentence to change your meaning and emphasis at will.

I've been trying to improve by making a conscious effort to practice it. I've been trying to blog and even wrote a book, partly to increase my writing skills.

The book that helped me the most is On Writing Well: The Classic Guide to Writing Nonfiction.

I also wrote a blog post about some of the lessons I learned:

https://www.jonashietala.se/blog/2023/11/25/writing_lessons_...

Developing Quality Technical Information - https://www.amazon.com/Developing-Quality-Technical-Informat...

My review + some notes - https://river.me/blog/book-review-quality-technical-informat... (it's very good)

Strunk & White is always good to thumb through: https://archive.org/details/TheElementsOfStyle4thEdition The Wikipedia has links to other copies, like on Project Gutenberg.

Anything by Diana C. Reep. Technical Writing: Principles, Strategies, and Readings is particularly insightful:

https://www.amazon.ca/dp/0205721508

I can’t recommend Strunk and White’s Elements of Style enough.