How you write and speak, as much as how you present yourself in person and online, says a lot about who you are and, as the case may be, whom you represent. If you care at all about making a good impression, you should have your manuscripts, speeches, scripts, advertisments, websites, and other work, edited by a publishing professional.
Why a publishing professional as opposed to a friend, colleague, teacher, or other professional who should be (or at least seems to be) good with words?
It pains me to say it, but I have edited entirely too many manuscripts written or reviewed by teachers and professors--of English, mind you--as well as those who write for television, advertisers, and movies, whose work was not up to snuff.
As for other professionals who write a lot for their jobs, like attorneys, they may write well for their industries, but they almost always do not write well for publication.
Editors in publishing know Associated Press and Chicago Manual of Style guides like the backs of their hands. If they write for a specific trade, like the medical or mental health professions, they will also know the American Medical Association and American Psychological Association style guides.
A story must flow, regardless the genre. Editors who review book-length works understand this and know what it takes to make a book enjoyably readable, memorable, and clearly understood.
Conjugation, tense, and voice have entirely different meanings when it comes to writing, and grade school was a long time ago. Editors know their way around such tools and use their knowledge and experience to make you look and sound great.