It is very interesting to see all the different techniques people use.
I’ll add mine. Two things have worked for me when trying to relax or ease them into taking nice photos are: first, small talk and jokes. Usually I’ll make fun of myself or my wife (sorry hun). As for example, a couple I was photographing was telling about their plans to hike Yosemite.. I figured this was a good time to tell them about my fear of heights trying to climb half-dome and how my wife made fun of me.. (You’ll understand this is you’ve ever been to Yosemite). Another thing I do is constantly ask them questions that are open ended, questions that can’t be answered with a simple yes or no. When I do engagement sessions I always ask the guy to look at his bride and name the thing he loves the most about her or if there is one thing he would never change about his fiance, what would it be, this always gets the bride all giddy and brings a genuine smile on the face of the guy.
My second way of getting clients to relax a bit is to ask them to act out a scene relevant to the pose I want to capture, something simple. I just did some headshots last week and I ask the model/actress to pretend she was a at a bar and some attractive guy just gave her a smile across the room.. now give him a smile back.. a smile that would make him buy you and me a drink!
This was probably the hardest thing for me to do when I first started.. basically every personality test I’ve ever taken classifies me a an introvert. So it does take some practice, I can attest to the awkward moments I’ve had with my clients in the beginning lol
A way to get some practice is get some random people from craigslist and offer $20 headshots. Practice on them and treat yourself to lunch afterwards.