That's a good guide, but one thing I think it doesn't emphasize enough is the preface. If a book has a preface, that's usually where the authors make their case for why the book exists in the first place. It's worth paying extra attention to the preface, because it establishes the context of the entire work. The ToC tells you what's in there, and it might hint at why, and the intro might give you more historical background, but the preface is almost always short and sweet.