I was told, a couple of days ago, that my posture, is allowing gay guys to pick me as being Transgender.
From this, my friend actually guided me on how I should be presenting myself (posture-wise)

I've now been trying to work on pushing my shoulders down, and a bit back, and sticking my breasts out. It feels quite good, problem is, I have been wound up for so long that it's difficult to keep my posture correct.

Anyone else having posture issues ?

I found at the start of my transition/coming out period, that my posture, speech patterns and even my mannerisms were still held back because I was fearful of making people uncomfortable. It's been about a year and a half since I came out, and things just naturally opened up as I felt people becoming more comfortable with my changes.

(Sorry I prefer not to give backstories on these types of threads, but in this situation some information is necessary) I was guarded and closed off do to my upbringing. I had a long closet period of my life that was brought about by a very religious upbringing, and when my earlier manifestation of my childhood identity came out, it was addressed (in the wrong way). I ended up closing myself up pretty well into a shell, or cocoon. This carried into my 20s, until I finally came to terms and came out. After that, it took me about a year to become comfortable enough to, well, be myself. I see the "shell" (that I was in) as a bit sticky, so while I broke it and poked my head through, it took a while to clean it all off. I still don't think it's gone completely, and it probably never will be, but it's far enough gone that I am now comfortable being myself.

Just give it time, let yourself flourish. Don't rush things, you'll only make yourself sad because these things cannot be rushed, despite how much you want it to go fast.

So to explain it in fewer words. Yes I had problems in my earlier days. Now I don't, as I became more comfortable with the people around me, and they became more comfortable with me, everything started to come out naturally.

It never hurts to practice. But really the main thing to remember is, just be yourself. It'll all come out. (sorry I tend to talk a lot)

Posture is extremely important in my eyes. The way our bodies are made up, slouching is a dead giveaway. I usually just try and pinch my lower back slightly in and that usually helps me, without looking too forced.. at the same time it feels very good for the back! I don't actually concentrate on my shoulders either unless they feel tense.. I prefer to really relax them. Pinching the lower back and relaxing everything else seems to make my chest naturally sit forward.

I have posture issues, but they're getting better as I get used to being myself, as SamanthaFLA says.  It's kinda weird, actually.  All the effort on doing it right never helped, but now mental changes seem to be making it happen.