Upload & Sell: Off
Start off with, "It's not your job to take a good photo. That's mine. That's why you hired me!" That usually sets people at ease. Also, laugh a lot. If they feel awkward, if you genuinely laugh with your couple, they'll laugh too. It breaks the ice.
Jose Villa told everyone at WPPI last year about his ice breaker. The first thing he does is ask his cooupe to stand, eyes closed, holding hands. With their eyes still closed, he tells them to lean in and kiss each other. They always keys eyes, cheeks, noses, necks, hair. It's funny, and has worked on many couples I've worked with this year.