A long time ago, I read on from one of the first internet "T" folks that the key to passing was found in 3 things: face, hair and voice. So I always worked hard on those (the voice was especially hard). For me, personally, I think body shape is a key as well, but it doesn't take much. Just a bit of pad and a bit of tuck in the waist covers it. When I first started going out on my own, away from my close group of friends who had encouraged me, a friend who had really helped me tune my "public" side said "you look like a long tailed cat in a room full of rocking chairs! You look great! Relax...you're giving people a reason to scrutinize". It wasn't easy, but I took that to heart.
I would say, though, my biggest confidence comes from improving my voice. Yes, it gave me a lot of satisfaction when I cracked the code on it, but also it seems to disarm people if something else might be off in my presentation. To be fair, I don't have big shoulders, or any other "tell" that might ordinarily give pause, because I'm pretty far into the overlap between male/female body sizes/types, but you never know when you might have missed something.
