The video below is a clip of an entire series that John Mayer did at the Berklee School Of Music in 2008 (before Battle Studies, as the video will show.)
There’s good stuff here about songwriting, having compelling chords, fighting for good melody, etc. But the most interesting thing to me is when Mayer reveals a song he’s working on. (2:14 in the video.)
The groove he’s playing eventually became “Assassin,” what I believe to be one of the most underrated of all his songs. It’s cool to hear a song in its earliest form, but also interesting to hear a crowd having a very positive, visceral reaction to a song that isn’t even really written.