When is the last time you were totally silent and focused entirely on the sounds around you? You can do this anywhere and I highly recommend it.
If possible, plant yourself in a location with no human-made input at all. The closure to true nature, the better. Have a listen to the birds, of course, and the wind as it goes by your ears, but try to listen closer. What does the grass sound like as it brushes against itself? What’s the timbre like? Does it change? Are there any animal sounds in the distance (or nearby)? Is there flowing water?
Listen to noisy city clatter. Squeaking brakes, pedestrian crossing signals, talkings, yelling, shuffling. Try and pick out as many unique sounds as possible and focus on each one. See if you can find it again after switching to focus on a different sound.
Listen to nothing. Composer John Cage’s famous work, 4’33” has the performer not play for its duration. Subsequently, one can hear every little thing that would otherwise be covered up by a typical musical performance. Apply this anywhere.
Listen to music. Don’t only put on background noise as you cook supper or work on your taxes. Try putting on headphones and listening for new things in your favourite music you’ve never noticed before or forgot about.
Listen to little things in between. Not unlike 4’33”, try listening to all the tiny inflections in someone’s voice or notice how the fabric of their clothing swooshes as they move. If you’re lucky enough to be at a musical performance of any kind, notice any unintentional noises made in between songs or during instrument changes.
Try humming along and harmonizing with your coffee machine.