https://www.amazon.com/Writing-10th-Anniversary-Memoir-Craft...
1) On Writing Well - William Zinser https://www.amazon.com/Writing-Well-30th-Anniversary-Nonfict...
2) On Writing - Stephen King- https://www.amazon.com/Writing-10th-Anniversary-Memoir-Craft...
3) The Elements of Style - Strunk & White - https://www.amazon.com/Elements-Style-Fourth-William-Strunk/...
The two most important points are concise style and active voice. Both of these habits are critical for SEs to write concise emails, specs and commit messages. You will even see improvement in more casual day to day interactions (via slack, SMS etc).
Source: his biography On Writing (http://www.amazon.com/Writing-10th-Anniversary-Memoir-Craft/...)
The other book I'd recommend is The Pyramid Principle[2] by Barbara Minto.
[1]: https://www.amazon.com/Writing-10th-Anniversary-Memoir-Craft...
[2]: https://www.amazon.com/Pyramid-Principle-Logic-Writing-Think...