I agree with the above. I think it becomes a matter of "ki sensing" to me, that is, where the energy is going - up,down, right, left - and going with it not against it.
That said, I once browsed a judo book in a bookstore that had a simple idea in it: it said to mentally draw a line between your opponent's feet, then right in the halfway point of that line imagine a second line crossing it at an exact right (90 degree) angle - that's your direction of kuzushi, or "off-balancing." Try it for yourself, it's pretty good. Problem: 1) spend too much time looking at feet and you're history 2) hakamas