It's pretty tough for me to take off the shield, as you put it, and the more immature or judgemental the person I'm dealing with is, the harder it is. It's also difficult when they're someone I admire - I get too caught in trying to always say the right things and trying not to offend them. Even when my guard takes its rest, I continue to offer little expression for quite some time.
When I go outside, I feel like a plaything for some all-seeing public eye. I observe everyone, making sure that I'm not strange, making sure that I'm not embarrassing myself by showing my face in the light of day. I try to be in such a way as to divert attention from myself - this theme will manifest as boring clothing, and maybe half a slouch.
It's not as bad as it tends to feel, I'm sure, but I can't remember being comfortable with myself at any time. Prior to transition, I felt like a ghost inhabiting someone else's body... nowadays, I feel like a ghost inhabiting my own body, but I'm not very happy with how my shell turned out. I have strong feelings towards it, and these lead to paranoia, anxiety, mistrust, and distance when dealing with other humans.
It gets better for most, and even I can say that I can express myself more easily, more freely... but it's easier for some, and more difficult for others. The better you look for the part, the easier it tends to be... at least, for a coward like me. Sometimes I wish I weren't so apprehensive towards my fellow sentient creatures, but I recognize that my current position, of being so separated from the rest of my kind, is comfortable in its own powerful way.
Expression will come for those who want it, and quicker for those who put themselves out there and go for it. You can't efficiently work on becoming yourself by yourself, strangely.
