I've sort or 'studied' women when ever I'd get the chance (at work, walking in a mall, on TV). My 'research' has led me to the theory that it's not the obvious signs that would make a MtF CD stand out as a man.
Granted, the deep voice, protruding adam's apple, lack of 'plumpness' in the face and appendages (due to the thinner fat layer), or strong brow ridge could very well peg you. But, being 'feminine' is more than that. To be passable, I think that that you have to nail the feminine movements. To me, this means:
* When walking, keep your back vertical (or 'plumb', as carpenters say it); also, keep your shoulders back (i.e. in line with your back). Keeping your elbows close to your body, perhaps 1 or both forearms out a bit (maybe swinging), also helps.
* When sitting, you don't have to cross your legs (I think that males' hips are built differently from females - I can't do it convincingly). Keep your upper legs together, and cross the lower part, slanting to one side.
* When talking to someone (especially another woman), gesture with your hands - iow, let your hands show your emotion. You don't have to bend it at a right angle all the time - just a bit of a kink could be enough. Also, touch is a good technique; touch your upper chest, upper leg, or shoulder. If the 2 of you feel 'endeared', you could touch her arm.
* You could also let other body parts show your emotion. Turn your head or tilt it a bit. Rotate your shoulders a bit (keeping your torso in the same position). If standing, position 1 leg differently, or bend your leg at the knee (just a quick flirty gesture). Bump out a hip and rest your hand on it, showing your pretty nails.
* Minor behaviors: play with your hair, file your nails, primp your clothes (e.g. for a shirt worn outside your slacks/skirt, make sure that the back is straight and flat), pull a mirror out of your purse and check your makeup & hair.
I think that getting the mannerisms into your behavior will keep you from suffering 'dude-in-a-skirt' syndrome. That's because feminine mannerisms are more important than being 5'8", with small hands and feet.