To reply to CIRE113's original question: you first must train your ear to hear the I - IV - V chords (tonic, sub-dominant, dominant). These chords combined contain every note in the scale. Do not concern yourself with complex chord changes.
Concentrate on hearing the I-IV-V changes only. When playing a new tune, learn the medlody and use those basic changes. Once you get that foundation and improve your ear you will naturally expand to more intersting chords.