Scales are an important and necessary part, but I agree with ZenoArrow - developing aural skills is the key. It opens up so many possibilities.
I haven't fully mastered those skills yet (still working on them), but learning just a little is like suddenly having a map while trying to find your way around a city. Before, you stumble around, stopping to ask for directions and taking wrong turns. After, you can plan what you want to do much more easily.
