Just putting this out there: Don't ask subjects to do something you're not willing to do.
I create a lot of imagery that requires the subject to act somewhat (or a lot) outside the realm of acceptable social behavior, which is tons of fun to do in the right environment. But how do you create that environment for people who aren't use to being able to let go of their serious side so easily? I start with leading by example. As a rule I refuse to ask anyone to do something I am not willing to do myself. But Willard, some might ask, surely you don't mean absolutely everything do you? I mean, stand in high-heals in a bikini watering a dead lawn? Yup. I would. Artistic nude? Check. Selfie of you flexing topples in front of a mirror? Done. I don't care what it is. If its a good enough idea then I had better be able to put myself out there for it. How could I ask something strange or intimate of someone if I am not willing to do it? It doesn't make any sense to me and more importantly, my willingness to do something off the wall softens the idea for my subject and allows them to quickly become comfortable with being silly. Its easier to do something when you know you someone had gone before you. Ever been to a water park with one of those 200ft almost straight drop, scary as hell slides? All it takes is one person to take the lead and try it, once people that otherwise might never try it see that it turned out fine they gain some courage and give it a try and usually enjoy themselves. So do yourself and your subjects a favor by not asking more of them than you are willing to give yourself. And when that strange idea comes up and its something you even you might be a little uncomfortable with, do a test shoot with yourself, get comfortable with it, grow as an artist and human, then take that experience with you to the actual shoot and your subject will loosen up, have fun and maybe even give you something better and more crazy that you could have thought up on your own.