Get yourself a tall mirror, hang or put it against a wall in your longest room (you're going to need a good amount of runway so you can walk towards the mirror), walk towards it, go back and repeat, a hundred times or more if you have to (actually heels were mentioned, try it if you have any), keep doing until you look right (what you want is to mimic the average woman, not runway model, nor the girl with the bad posture), then do some more until it feels natural. Hips first, shoulders straight, relax.
Remember how you practiced with the mirror, now try it outside (when you feel ready), take a walk just anywhere, constantly mentally check yourself (but don't look like you are) when walking that it feels as it had when you'd done it in privacy, if you aren't getting any strange looks then you may just have it, remember it, eventually you won't have to think about it, you'll just walk that way automatically.
I'm a very fast walker, but also have long legs, so long strides as well (like a giraffe), but I think I walk feminine enough for a woman in a hurry. My posture when standing and walking is actually pretty good (I used to hunch a lot in my teens), but trying to fix how I sit when at my desk because I tend to lean on it too heavily, bad for the elbows, neck and back.
Not all cis-women have good posture, but obviously you don't want to be one of them. They can get away with however they stand, walk or sit with no question to their gender, you (and I) on the other hand, lazy posture or walking like an upright gorilla can lead to questioning stares regarding your gender, unless you so happened to look so convincingly cis-female that you simply appear to be a tough girl, maybe even mistaken as butch, but that kind of image only works with the right clothes too (as well as attitude, hair style, whatnot), not a fancy dress with heels or such.
