h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I personnally recommend 'Teach Yourself Writing a Novel' by Nigel Watts who teaches creative writing in the University of East Anglia, the same course that Malcolm Bradbury used to teach.

Bob Shaw (SF author) wrote "How to write Science fiction"

The scriptwriter of the most popular Star Trek episode ever "the trouble with Tribbles" also wrote a book on how to write SF and Fantasy but I've forgotten what his name is (something like Erroll Gaskell or something) or what the book was called ('Worlds of wonder' or something like that).

There's also 'On Writing' by Stephen King which doesn't necessarily teach you all you need to know as there are so many books out there but he puts his own stuff in. It's more of a personal perspective on writing which makes it slightly more approachable but also let's you know what the process of writing is actually like.