Some writers find that they don't know their themes until they've finished the first draft (I am one). They then rewrite with an eye toward balancing on that tightrope: not too contrived, not too rambling; does what I'm saying about the world below me actually add up to anything? Other writers pay attention to these things as they write the first draft. Either way, an awareness of the macro and micro levels of theme can provide one more tool for thinking about what you should write, and how.

In commercial fiction especially, everything in the story usually contributes directly to the plot The shorter the story, the truer this is

Anything said in upper-crust British automatically sounded intelligent.

Religious reverence for one's own job, even if the job is worth doing, is a sexual turnoff.

Changers 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.

There are two wrong reactions to a rejection slip: deciding it's a final judgment on your story and/or talent, and deciding it's no judgment on your story and/or talent.

Technology is Darwinian. It spreads. It evolves. It adapts. The most dangerous wipes out the less fit.