I recommend getting three books and to begin writing at least 500 words per day distraction free (technical, fiction, stream of conscious):

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).

Also see Stephen King's memoir "On Writing" : http://www.amazon.ca/On-Writing-Anniversary-Edition-Memoir/d...

Stephen King's rule is that the second draft of his book should be ten percent shorter compared with the first draft.

Source: his biography On Writing (http://www.amazon.com/Writing-10th-Anniversary-Memoir-Craft/...)