Hi Nero
Sorry to come late to this party, but here is a bit of hopefully helpful input from the dark side.
Like others have said, visual appearance is of course a part of this but I'm sure it also comes down in part to the way one projects ones inner mental state. If you look at the photo in my Avatar you will see Alison, my partner and I. (she is the blonde). In many respects Alison has a better figure than me, almost perfect shape fantatstic legs, and great looks given that she is over ten years my senior.
I by contrast make minimal effort with my appearance. yet whilst my success rate in pretty well 100% Alison's is probably only 85 or 90% - still pretty good but irritating given that, by purely visual means she is by far the more convincing.
So what is the difference. Mainly I would say deep inner core belief and perhaps a subtle difference in subconscious conditioning. I, by immense good fortune, having largely grown up in my desired gender never doubt that I AM female. Not only do I take it forgranted that people will recognise that, but because of the way I was drilled at school I probably also subconsciously send out matching non verbal signals.
For example because of my social class, I had to go through deportment classes, and learn proper "decorum". I was treated, in many ways, more strictly by my parents, was more protected than my male friends, and perhaps allowed less early freedom. Somehow that level of belief and programming does project itself.
By contrast Alison, who transitioned later in life, had a career in which she was drilled to project male self-confidence and strength. As a result she has tacitly accepted that she will occasionally get mistaken, so indeed she does.
In part it's a bit like pulling onself up by ones own bootlaces. In order not to be misread one has to get into the mental zone where subconsciously one is absolutely confident, which of course is a catch 22 when you aren't always making the grade.
But I have absolutely no doubt that you will get there.
