Writing Science Fiction that Sells
A book review.
by Ben Bova
This is a readable, straight-forward exposition that teaches useful ideas very well. I'm not a wild fan of Bova's fiction, but I certainly read this from front to back. I highly recommend it for one reason above all - I'm able to keep his ideas in mind as I'm writing, and I've found them enormously helpful. My fiction is now better.
I can also recommend a counterpart to this one; it's Becoming a Writer by Dorothea Brande. Bova's book is on the technical matters. Brande's is on the intangibles.