How to Write Tropes
If you write, you’re probably already using tropes. It’s almost a guarantee. If you write fantasy stories, for example, you’ve been inspired to do that by the stories that you’ve read in the past; and even by stories you don’t even remember, or stories you haven’t read that influenced the stories you did read! The dragon on a hoard of gold, the legions of teeth-gnashing goblins, the courageous elf archer – all of these are tropes in the fantasy genre with a long history. Similarly, realistic fiction has its own tropes, as does poetry, nonfiction, and even everyday conversation. It’s almost impossible to write, speak, or create art without drawing on tropes!
So it may not take any effort to use tropes in your writing – it’s part of the writing process because our heads are already full of them. The key to using tropes efficiently and creatively, without sounding cliché, is to use them in a way that shows that you’re aware of their stereotypical usage, and either honor their tradition or play with them more creatively. For example if you’ve got a dragon sitting on a pile of gold, either do it as well as Tolkien, in classic style, or do something original with him, such as making him lonely.
When to Use Tropes
Tropes are a part of language, and they occur in every kind of rhetorical or creative effort. For example, “analogy” is a trope that appears in creative writing, poetry, formal essays, film, art, and theater (and arguably even in music and dance!) Other tropes may be more specific to certain context. For example, “space is the sea” (see Examples of Trope in Pop Culture) is a trope that only in science fiction. So the question of when to use tropes depends entirely on which trope you’re talking about.