Leading
An important idea that I have learnt the hard way is that when you are leading you are really just initiating a movement, but it is her job to execute it.
When you are connected then you both have your own personal centers, and then you have a mutual center which is where your hand connection is.
Imagine there is a spring between your personal center to the mutual centre. Any lead involves stretching or compressing that spring by moving your personal center only, and keeping the mutual centre where it is.
The common mistake is to initiate a lead by 'shoving' the mutual centre. The only way she can respond to this is by stiffening her own 'spring' which ruins any fluidity.
Here's an example where the man is leading the lady to take a step backward. The ideal situation is that he compresses his 'spring' by initiating his forward movement, so he has started moving, but the mutual center is completely still relative to her. That is, the distance between his personal center and the mutual center decreases, and the force increases.
Next she feels this change, and allows her spring to compress by letting the mutual centre to move toward her. At this point she has not moved her personal center at all, but she is responding to the increase in force in the connection and preparing to move.
Finally, when she is ready, she uses the force provided through the connection to move her own personal center backwards until the two springs are at their neutral lengths again, the force is back to zero, and both people are ready for the next step.
This creates this beautiful delayed look to the movements. It also means she can control when and how she starts to move her own center and she can keep completely on balance.
Hope that is of some use to people, and that you don't disagree to much!