Effortless stereotypical Feminine body-language and behaviours are caused for the most part by having an entirely feminine brain. I know that in my case parts of my brain were feminised in utero, while other parts developed along male lines. My sister from whom I have learnt a lot, displays all the gestures, body-language, and facial expressions of the typical female and she does so completely spontaneously and naturally. She didn't have to study other girls and women for a second in order to become skilled at presenting at all times and in all situations gestures etc that will mark her as undeniably female. The reason her every movement. gesture, and facial expression are so natural and effortless is I believe entirely due to her having an entirely feminised brain.
I am not suggesting that anyone should stop trying to suppress their genetic gender body-language etc or stop studying genetic males/females for tips. What I am suggesting is don't become obsessed with gesturing like a woman, or walking like a guy. Don't analyse your target gender's mannerisms to death. If you go too far down this road it is unlikely that you will ever succeed in getting your 'act' down pat, and be assured it will be acting and not expressing your inner man/woman. In fact if you look to other people to be giving a gender 'performance' you will just succeed in attracting unwelcome attention and criticism towards you.
It is not the gestures and mannerisms per se that are important but the mindset that produces the body-language. Cisgendered people have an unshakeable believe that they are male of female and this along with years of exposure to the effects of hormones and physical anatomy - to say nothing of male or female socialisation - produces all the gestures, mannerisms, body-language, facial expressions, and ways of walking. Do you have that unshakeable belief that you are your target gender? Can you honestly say that there is no one and no argument that could convince you that you are not female if you are an MTF. Or that you are not male if you are an FTM? It is that unshakeable belief in their core gender identity that gives men and women complete confidence to freely go about in the world and be themselves without fear of ridicule or physical and or psychological attack.
One of the reasons I believe that transsexuality is NOT either a paraphelia or a 'mental-illness' is that despite the fact that we have very little of the hormones of the so-called opposite sex, and despite years of heavy socialisation to think, act and behave in our perceived (by other people) gender, we still insist to other people, or only just ourselves that despite all appearances to the contrary we are actually female/male (delete the one that doesn't apply to you). I think this powerful and highly persist belief comes from our soul, or if you prefer it comes from our subconscious mind. This is something to take comfort in when other people seem to go out of their way to deny your truth.
To become as naturally female as my mother or my sister or effortlessly male as that man in the street. You have to develop an unshakable belief in your gender and insist upon expressing it at all times. Long-term exposure to hormones will undoubtedly help with this process. Oestrogen and testosterone if taken long-term will slowly but surely 'rewire' the brain along female/male lines and you may well find that you are increasingly expressing yourself physically more and more often effortlessly and unconsciously as a man/woman. Naturally produced body-language will go a long way to convince other people that you are your target gender even if there are some signs to the contrary. If you are close to being passable in height and appearance then striking a series of carefully contrived, but artificial poses will ruin all your efforts with clothes, hairstyles, make-up etc.