First, I should probably 'fess up. I had already had some (non-food related) articles published and was an intermediate blogger before I picked this book up.
I found this book extremely useful as I wanted to begin writing about food but could miss out sections or skim read those that dealt with areas I'm already comfortable with. Yet, there are still a couple of sections like 'writing your own cookbook' that may become more useful down the line.
This really is one of those books that needs to be re-read at regular intervals as you develop.
For a beginner this book is probably overwhelming - you need to feel comfortable writing so I'd recommend a book focusing on writing skills to complement this book. I'd recommend this one: Creative Writing
For intermediates, like me, there is a ton of guidance in here that will help you get started specialising in food writing. The great thing is you'll probably find yourself nodding as you read through the stuff that's good for beginners - reassured you're on the right path.
And for the advanced readers...it will point you in the right direction for working towards authorship yourself.