I've read a fair few books on writing fiction, but this one is probably the best. Dorothea Brande's "Becoming A Writer" tells you how to think like a writer; this book explains how to write like a writer.
I thought I knew the bones of writing technique already, but this book contains so many insights that I often felt it necessary to break off reading in order to consider fully what I'd just read - not because the writing is not clear and easy to read, but because the points the author makes are so momentous.
Many writing guides talk in generalities or talk down to the reader, but this one isn't like that. Just one word of warning - I think the best of the book is in the middle and end, so don't be too impatient when reading the introductory chapters.