When I was in college and grad school I learned so much from my teachers, coaches and conductors but I gleaned an enormous amount of information by listening. My friends and I would spend countless hours listening to recordings together and discussing what we heard. In this way we learned about style, phrasing and use of language. "Did you hear how he lingered on the M of that word?" "That pause was orgasmic," "I love how she chose to float that high B flat." We shared new rep we'd discovered, we learned about artists old and new and we learned about the history of our art form.
One can also learn about technical strategies other singers employ: "She belted that note but mixed that one," "He did that all in one breath," "She modified that vowel."
If you want to learn from the master of this way of listening watch some of Seth Rudetsky's Deconstructions. Then, start deconstructing things for yourself. Listen with a discerning ear, not the critical, I'm-going-to-leave-a-nasty-anonymous-comment kind of way which is all to prevalent these days, but, with the intention of learning and understanding.
Now - go make some playlists and start LISTENING!