Today we're going to explore two useful concepts: mirror characters and foreshadowing. Even if you're not familiar with the concepts, chances are you've used one or the other in your writing.
A mirror character is just what it sounds like: a character that acts as a reflection of the protagonist. It can be a mirror that shows the character the way forward, as in a secondary character who knows the "truth" the character is searching for (as in character arcs and "the lie the character believes"), a contrasting, opposite character, or it can be a dark mirror, usually an antagonist with a similar background, showing where the protagonist could be with a few bad choices or if she gives in to the "lie." Scrooge and Marley from Dickens' A Christmas Carol are a Christmassy example of this, a few others are Frodo/Gollum from The Lord of the Rings and Harry/Voldemort from Harry Potter. Mirror characters often embark on parallel plots, like Han and Luke in The Empire Strikes Back. Mirroring is a useful tool; in addition to characters, you can mirror plots, scenes, and dialogue to add subtext and depth to your story.
Have you ever read a story where the plot twists seem to come out of nowhere? One way to fix this kind of issue is foreshadowing. It means dropping a hint of what's going to happen into an earlier scene. Remember the dead direwolf in the beginning of A Game of Thrones (spoiler alert!) that just happens to have the exact number of pups as Ned Stark has children? And the bit on the trip to King's Landing where Joffrey gets attacked by Arya's direwolf (totally his own fault) and insists that it be killed? Both of these foreshadow Ned Stark's death at the end of the novel. I feel the best way to use this technique is to keep it as subtle as possible. The best foreshadowing works on a subconscious level; the reader doesn't even notice it but it can make the most outlandish plot twists feel inevitable.
For today's 350 words, add a bit of foreshadowing into your story or explore mirroring as technique.