The best training I ever had for learning tunes "by ear" was a weekly session with the Pretty Shaky Stringband" in East Lansing, Michigan. We'd gather together, a mix of experienced and inexperienced players. A lead fiddler would announce and start a tune and everyone one try to catch up. Occasionally a guitar player would shout out some chords. Initially, all the tunes sounded pretty similar but after a while I would figure out what the chord structure was, and how best to position my capo to play along on my 5-string banjo.

Cheerily,
Charley Noble