"How to Teach Grammar", like others in the series, (How To Teach Pronunciation (Book with Audio CD)), is an excellent and very practical resource. As always, it is written with the classroom teacher in mind, and Scott Thornbury has written a very accessible and very useful book.
The book covers some broad areas, such as why teach grammar and even how "NOT" to teach it. Thornbury gives three broad approaches: teaching grammar from examples, texts and rules. He also covers issues related to correcting it, practicing it and integrating it through a couple of different approaches, (such as PPP and skills-based teaching).
I found the book an excellent resource for new ideas and getting a fresh look at a complex issue. If you have been a teach for awhile and happen to be looking for a renewed outlook on grammar, this could be a book that you need to see. I loved it, and still refer to it a lot.