6. Writing science fiction is not a license to play fast and loose with science.

This is one of the most important things that a science fiction writer can learn; it's one that some do not.

The story should be consistent with what we know, what we think we know, or what we might learn about the universe and how it works.

Writing a story in which a huge Jupiter-sized planet has a gravitational attraction one-sixth of Earth's would get the story into any editor's "circular file" faster than you can say "where no one has gone before" - unless a plausible explanation can be provided.

Unfortunately, some science fiction writers never learn this.  (Did you notice the errors in "Men in Black"?)

With these things in mind, let's look at some of the characteristics of good science fiction.