Everybody can improve their writing with the help of these useful guides. Click on the links to buy these books on Amazon.
The Elements of Style by Strunk and White
On Writing Well by William Zinsser
The Penguin Guide to Punctuation by R.L. Trask
Style: Ten Lessons in Clarity and Grace by Joseph M. Williams
The Oxford Essential Guide to Writing by Thomas S. Kane
McGraw-Hill Handbook of English Grammar and Usage by Mark Lester
And last of all, a guide about targeting audiences. I wrote this for Earth Law Center early in 2018. The guide is on PDF and available to you for free. No registration required.
A guide for Earth Law communication by Helen George