Booher's Rules of Business Grammar is a handy reference book for grammar rules in the workplace. The larger style guides like Covey's and Gregg's, although great guides, are large and cumbersome. Booher's is small enough to keep right by your computer for ease in picking up and reviewing quickly. Because it addresses the most common errors I see in business documents, most of what I need is at hand. I don't have to search indexes to find what I need, and struggle back and forth until I find the exact section. I suggest this book as a handy, dandy business tool.
I bought this book to help improve my business writing. I knew I could do better, but wasn't sure where to start. When I read the book, I realized that I had more areas to improve in than I originally anticipated. (yikes!)
It was a little overwhelming; I wasn't sure how to tackle correcting my bad habits. I have to write quickly at work, so I don't have time to dissect and overthink my grammar. I decided to work on three areas that were my "biggest offenders": mixing tenses, redundant words, and active vs. passive voice. Once I consciously worked on these areas, they started to come more naturally. Now I am working on the next group of "bad habits".
My advice is to not get overwhelmed; no one is perfect. Taking incremental steps to improve your writing skills will pay off. Good luck!