Listen for things that tell you when you are in a certain place. For example, listen for things that will tell you you're "in the classroom". Some things might be:
florescent light buzz
ticking clock
sounds of traffic or people outside or down the hall
turning of pages
writing on whiteboard
tapping of pencils
typing on keyboard
These things can all be combined to give the viewer a sense of where they are.
Imagine some other locations (your home, a store, a street in your neighborhood, on a hike in the mountains), and what sounds you might want to include to create the impression of being there.
in the forest (birds, wind through the trees, running water
in a shopping mall (footsteps, music, kids laughing, a fountain)
outdoor cafe (traffic, police sirens, clinking silverware, people talking)
Human Sounds or Giving "life" to scene
Breathing
Footsteps (are they on a hard floor, maybe in a swamp with "squishy" steps, running thru dirt or gravel, etc)
Movement
Vocalizations ("ooooh", "aaaah", "hmmmm", not necessarily words unless they actually want the object to "talk", sniffles if it has a cold, etc)
Learn more about creating sound effects for film, The Art of Foley
"Though we might think of film as an essentially visual experience, we really cannot afford to underestimate the importance of film sound. A meaningful sound track is often as complicated as the image on the screen. The entire sound track is comprised of three essential ingredients: the human voice
sound effects
music