Once my subject has relaxed into the shoot, that's when it gets fun. The effort of creating rapport over a short period of time (as fast as possible, really) pays off when the reactions become natural, when people, with my assistance, get on my wavelength.
People come in with a set of expectations, and more often than not, my goal is to subvert those expectations. Give them an experience better than the one they were anticipating.
Sounds complex and overwrought...it's really about having a good time, and creating the environment for my subject to have a good time, as well.