On Writing Well: The Classic Guide to Writing Nonfiction by William Zinsser: Probably my favourite book on writing, this perfectly illustrates the oft-quoted adage ‘show not tell’: a book on writing well that is written well. It’s a wise, clear classic.
Writing down the bones: Natalie Goldberg: The book I first read in starting out on my creative writing journey. So packed with imagery and inspiration that I could almost eat some of the pages.
On Writing by Stephen King: its subtitle, ‘a memoir of the craft’, accurately describes what you will find inside. A mixture of autobiography and writing advice from a great story-master.
Story by Robert Mckee: Classic book on the art and craft of storytelling on screen (as referenced in the film Adaptation).
Thesaurus: no one intending to put words onto paper or screen should be without one. Reach for the most specific word, not the nearest word. Have a physical one to hand (not just the tool on your computer). Mine is a big heavy Penguin thesaurus but spend some time in the bookshop finding one whose layout suits you.