You can start anywhere, literally anywhere. Just open the book at any page and go; truly, it is that easy. I came across this book when taking an English Upgrade course in writing at the University of Toronto back in the 1970's - subjunctives, subordinate clauses, adverb clauses, appositives, punctuation, and on, and on, and on ... . My marks went from C's to A's.
The book eventually fell apart in my hands from the constant use and reuse as I referred to it when I needed it. I referred back to it all the time, simply because some of the topics are, to some extent, obscure and not easy to remember without constantly using them. Is your boss picking on you because you can't write? Are feeling out of the game because you can't get a handle on English grammar? - get the book (and use the book) and get your boss of your back and maybe impress your boss's boss as well.
I just ordered a new one, because my wife speaks English as a second language, and she will have no trouble using it what so ever.
It is a gem, a prize, and a wonder.