Let's not make this sound TOO easy, though. For MOST folk/trad stuff, these strategies will work. But as your listening expands, so does your awareness of the complexities that are out there. I don't know the song you mention, but I've spent many a frustrated evening trying to break down the notes in an a flat minor diminished add 9 and hold the mayo.

And that's even before you run across open tunings and up-and-down the neck fingerpicking!