Like a lot of folks, I will usually chat it up with the subject... often about totally unrelated things. Also, for the first 15 minutes, if we are outdoors, I will just shoot randomly and tell them that I am just getting everything set. That gets them used to the camera, and I often get some good keepers because they don't feel like they are 'on the spot'.
One other thing I do is encourage them to bring a family member or friend. Someone earlier in the thread remarked that great photos can come when the subject is not aware of you shooting. Many times, I have seen the subject just be talking to their child / father / friend and share real smiles and laughs... that tends to yield a pretty good photo.
...at least that is the stuff that I do...
