For me it depends on the moment and who I'm around. During casual conventions, most of the time I will be your generic "cop" trooper pretending to be minding my own business, almost never removing my helmet because my hair is a mess anyway
When around buddies, we like to relax and be funny with each other which makes people more comfortable around us.
My favorite "acting" moment is around kids, though. Especially the shy ones, being a shy person myself I find that my Stormtrooper character brings out the "hero" in me and so I care a lot about the impression I give to children. I won't hesitate to take their hand and talk to them while their parents take pictures :')
My advice to you is to find the attitude that makes you feel most confident, and use that feeling to act as naturally as it comes. Be yourself! Kind of clichÃ© but it's what it comes down to. There is no need to be afraid to do anything since, at the end of the day, anything you'd have done would have been awesome because you did it as a Stormtrooper.
It takes time, yes (over a year for me, starting as a biker scout,) and recently had to get used to trooping as a TK which made me start over as a comfortable trooper.
What I noticed made people uncomfortable was the slight "sideways look" with the helmet. It's more socially acceptable to look at them straight and wave/nod/do something with your arms. Because our faceplate is intimidating, it's important to distract the non-fan public from it with body language. Always choose slow, deliberate motions as opposed to quick, unfocused, hesitating gestures. The way you move your upper body is important, that's what takes practice.