This is a book on developing the habits that enable a writer to write. It's not about the technical details (such as John Braine's How to Write a Novel), but rather concerns the nurturing of the mind-set required to actually create. The author - and this stuff predates modern psychology - speaks of the creative unconscious and the conscious that acts as its shaper. These two components are discussed at some length, along with simpler stuff such as organizing your time so that you regularly set aside time for writing.
It's an easy read, and contains a lot of useful thought. I recommend it as a counterpart to the many technical works that exist.
This is an older book - the oldest I've reviewed. The initial revision dates way back to 1934. But the content remains remarkably useful in our time.