I haven't read all the above postings, but learning lots of songs with lots of different chord changes really trains the ear to being able to anticipate what chords are needed. Like many of the above posters, knowing your chord families ( I,IV,V and relative minors etc is very helpful),also, with folk, there is the I and bV11 change e.g. if D were chord I, then many folk songs move to C at certain points.