I really like putting in little throwaway details which later become important. Here are a couple of (deliberately vague so as to avoid spoilers) examples in Elf Noir:
First, when Arq and his fellow enforcers go to the Bouncy Tart to try to solve a murder, they come up with multiple clues suggesting four different avenues of inquiry they could pursue. The one they choose leads to them uncovering the information necessary to solve the case, at least as to the immediate details of the murder.
Satisfied with the resolution of that matter, Arq devotes his time to another matter - i.e. the main plot of vengeance.
He won't find out til much later that one or more of the other avenues of inquiry would also have produced useful and important information about the murder.
Second, there are multiple references to Arq being lucky casually slipped into the narrative. The cynical might suspect it's a backhanded recognition of his "plot armor" 🤣🤣 but it's possible that it might actually be something more
A couple of commenters have noted little bits of foreshadowing I put in, which makes me so happy, and when the foreshadowing comes to fruition, they are definitely getting a shoutout in the comments!.