Author Orson Scott Card knows how to write Science Fiction. He won the Hugo and Nebula Awards two years in a row-- first for Ender's Game and then for Speaker for the Dead. He is the only author to have won both these prizes in two consecutive years. Experience does not always translate into a successful how-to book, but in Card's case it works wonderfully. How to Write Science Fiction & Fantasy was the first book that I picked up when I decided I wanted to venture into the fantasy genre, and it was a wonderful investment.
This book is geared towards Science Fiction writers more than Fantasy, but if you are interested in either genre it would be worth your time to read. He begins by defining the boundaries between the segments of speculative fiction, particularly between Science Fiction and Fantasy. He breaks down the rules to their simplest form: "Science fiction is about what could be but isn't; fantasy is about what couldn't be."
Then Card moves into one of the most important parts of creating these types of stories-- world building. Even if you never mention them in your story, you have to define the rules of your world. You have to know how the space travel or magic work, and what their limitations are. If the fantastical elements have no consequences and no definition, they can quickly become a deus ex machina and pull the reader out of the story. You can only expect your reader to suspend their disbelief for so much; you must have a grasp on the rules to keep them interested.
One section, number 4, is titled simply "Writing Well" and I recommend it for folks of all genres. While the examples it uses lean towards Card's own genres, the topics are basic and necessary, such as naming, piquing the reader's interest, and exposition. He does a wonderful job at explaining how to relate information to the reader without falling into the trap of the "info dump."
How to Write Science Fiction & Fantasy will put many other books on your "must read" list, as Card makes liberal use of examples from his own life and other authors. Octavia Butler and Ursula K. LeGuin are frequently quoted and paragraphs from their work are dissected. By using other books to illustrate his points, Card allows the reader opportunity to continue studying beyond the cover of his book. He gives his audience direction.
If you want to write speculative fiction, Orson Scott Card's books should be on your shelf anyway. This one is a wonderful addition, and I am grateful to him for being willing to share his knowledge and experience with new writers!