Neil Gaiman advises where you can look for ideas--or rather, why ideas really aren't the hard part.
Lou Anders explores those gazillions of subgenres and actually makes them make sense. (Ever wondered where the dividing line is between hard sci-fi and soft? And what about cyber-punk, or high fantasy?)
Ursula Le Guin? Yes, she's here too, one of several authors answering interview questions.
There are chapters on killer beginnings, middles (and middling through), what's special about sci-fi/fantasy endings. Orson Scott Card discusses rhetoric and style. Pamela Sergeant offers the sort of dialog advice that every author should read.
Character, emotion, aliens (they're characters too), Larry Niven, Harry Turtledove, Joe Haldeman, Alan Dean Foster... all the greats! And all the chapters have information, help, advice, encouragment and more, not just for sci-fi writers but anyone hoping to entertain an audience using words and imagination.
Perhaps I should have asked do you write or want to write? I had just started writing Writers Workshop of Science Fiction & Fantasy but now I can't stop. This book is good! (And it's got great illustrations too)