Every paragraph should accomplish two goals: advance the story, and develop your characters as complex human beings.
Nancy KressTechnology is Darwinian. It spreads. It evolves. It adapts. The most dangerous wipes out the less fit.
Nancy KressWhat characters do must grow out of who they are, and who they are is, in turn, influenced by what you make happen to them.
Nancy KressChangers are characters who alter in significant ways as a result of the events of your story. They learn something or grow into better or worse people, but by the end of the story they are not the same personalities they were in the beginning. Their change, in its various stages, is called the story's emotional arc.
Nancy Kress