Have you ever heard the term "it feels lived-in" used to describe a movie or TV setting? For example, in Star Wars, lots of the sets are scuffed and worn--it makes each place look like it's existed forever. In Crazy Ex-Girlfriend, Paula's kitchen countertops are covered in junk, like Paula and her family really live there and we just get glimpses into their lives.
You can do the same with your writing. Little traditions can make your characters' lives seem more real to the watcher (er, reader). When writing descriptions, remember that people aren't perfectly neat--describe their unique messes! Anything you can do to make your fictional world feel like it exists outside of your story will help your readers to sink deep into your work.
What techniques do you use to make your worlds (contemporary or otherwise!) feel lived-in?
Do you need an extra set of eyes on your query letter? I'm offering up some critiques! If you're interested, let me know in the comments! I'll select a few people to win critiques.