depicting shy can lead to awesomely poignant poses. however, even if youre going for stiff, it has to be organic. Humans only look robotic when actually trying to look exactly that. think about how the entie body truthfully reacts. im a shy person. my shoulders raise and turn inward, , back bent forward, my head is slightly downturned, feet slightly inward, i often cover one arm of the other tightly, my facial expression usually has a tensed brow. (but there are so many more complex ways to represent all kinds of emotions. For instance, sometimes when anxious I might try to appear more confident with a squarer poster, head held up high, yet anyone with good body language observation could see on my upturned head is still a face struggling to be relaxed) see, it's a lot more organic than robot straight everything and a blank expression
it's up to you to decide how much life you want to breathe into it, as well as how you but you should at least strive for a basic representation of what emotion you want to achieve when expressing them.
sorry for the wall of text