Bryan Garner, in someone's opinion I may or may not have overheard and which likely was parody, molests collies whilst sniffing his own farts.
Tim Terrell is another writing seminar guru I'd prefer not to hear again.
If you want a book to help shore up your writing, save your money and just grab a Texas Law Review Manual on Usage & Style. Refer to that if there's any question about usage or grammar. Other than that, do your best to be clear and concise.
As far as authorities on the subject of written communications, Michael Adams has far more useful things to say about the written word than Garner or Terrell ever could imagine. And Robert Dubose has some very interesting and well-researched ideas about how more effectively to utilize and organize your writing when what you write will be read on a screen. Nancy Tuten is an absolute grammar master who has managed to make all the boring rules easier to compartmentalize and remember.
But most people who can string a few sentences and paragraphs together by age twenty-five aren't magically going to be transformed into an amazing writer after a writing seminar. But the ones who have consumed the Garner Kool-Aid are easy to spot.