Work on small sections, maybe only a measure or less to begin with, and really listen from note to note. Shift your attention from one thing to the other: the notes, the chords, the quality of each sound, how they blend or don't blend - get miniscule. See if you are tuning out in between. We usually spend most of our time thinking about other things when we do things, and only pull in our attention here and there. It's a real eye opener.