Every story or narrative contains certain cliches, certain archetypal themes that occur time and again and whose presence defines a genre.
If, to give a ridiculous caricature of an example, a story features an alcoholic ex-detective renting a grungy office, whose hired by a glamorous blonde in furs and high heels to check on the wealthy husband she has a loveless relationship with, you know that’s a Crime Noir story.
In writing science fiction (or science fantasy, whatever the case may be), certain tropes are used, and again, the types of tropes determine the type of science fiction (space opera, time travel, cyberpunk, steampunk, parallel worlds, post-apocalyptic, etc). In general, tropes have to be of a technological or pretend-technological nature for a story to qualify as science fiction rather than fantasy. If for example, there are spaceships, it’s science fiction. Dragons, it’s fantasy (however it is sometimes possible to have both and still be science fiction)
The following is a partial list of tropes that feature that are commonly found in space opera type science fiction
- Alien artifact
- Badass Babe: “Hey Vasquez, have you ever been mistaken for a man?” “No, have you?” (Aliens)
- Badass Monk – “I Am One With the Force and the Force Is With Me” (Chirrut Îmwe, Rogue One, Star Wars)
- Big Fucking Ship – because every space opera needs gigantic hunks of metal and fullerene studded with guns and greebles
- Bounty Hunter
- City Planet
- Cool Spaceship
- Desert Planet
- Eldar Race
- Galactic Empire – or Imperium, Federation, or whatever. May be utopian (Star Trek), dystopian (Star Wars, WH40k), or anything inbetween
- Motley band of misfits – e.g. Blake 7, Red Dwarf, LEXX, Farscape, Firefly, Cowboy Bebop, Guardians of the Galaxy, Rogue One, et-cet-era.
- Ocean Planet
- Space Gods
- Space Habitat
- Space is an Ocean
- Scum and Villiany – “You will never find a more wretched hive of scum and villainy. We must be cautious.”
- Space Marines – because every space opera needs space marines.
- Splice (manimal)
TV Tropes – a vast and highly addictive website, featuring just about every trope known to man, and then some.