I think passing is somewhat relative and that few transsexuals pass 100% of the time. You may have big feet or hands, adams apple, be too tall or some small detail that may give you away. I think that the more details you get right and the more feminine characteristics you master, the less your big feet, hands or whatever other problem you have will matter.
Most women can ignore all the things I address below and still not get their femininity questioned but when a transsexual tries to pass, they have to try to stand out as little as possible.
I have a few thoughts and also some experience in how to pass that I base on my own experience and on talks I have had with the various people I see at the gender clinic.
Icons
Find some women that you think have style and class and study how they dress, act, talk and move. If you think that finding your icon is easy and instantly think of Gwen Stefani, Shakira, Marily Monroe, Brittney Spears or Elizabeth Hurley then scratch that idea. Neither of those are real women, they are icons and mass media products and anytime you see them they have been dressed, styled and made up by professionals. Find real women and study them, forget about the models.
Don't use women that men think of as perfect for your icons unless you think your part in life as a woman is solely to please men.
Style
Don't overdo the makeup. Most women use little makeup for everyday use and you should only use makeup to bring out the features that you have and not try to recreate your entire face until you look like a clown. Less really is more.
Do dramatic eyes OR dramatic lips, not both. It's the same rule that applies to jewelry; if you have eye catching earrings then you use a simple necklace or the other way around.
Makeup takes practice. Most girls start using it when they are in their early teens and most of them do an awful job with it. It takes them a few years to get it right and it will take you a long time too. Practice makes perfect. Take a class, practice at home, ask for help at the makeup store to help finding what is good for you. Most women in their 30's have 15 years of practice putting on eyeliner and it would be naive to think that you can learn to master it in two weeks. There are no shortcuts here.
Don't use a wig unless you have a problem with your real hair. Most wigs are easy to spot and you don't need hair all the way down to your waist to look feminine.
Clothes
Dress in clothes that flatter YOUR body and don't buy clothes that look good on someone who has a body nowhere near your own shape. Make sure the colours suit you, the clothes are the right size, in fashion and avoid wearing clothes that you think look good on their own but that doesn't really fit or suit you. Try the clothes on and if the piece looks good but doesn't fit you, don't buy it.
Dress your age. I can't say that one too many times. If you are 45 you will never be 15 again. That time has passed and unfortunately you have probably missed it. I know that's a bummer to a lot of people but in the real world 45 year old women don't wear schoolgirl outfits. Look at women around you that are your age and what they wear. Imitate, copy and steal ideas from women at your workplace, gym, nightclub or wherever.
Don't overdress. Women usually don't go shopping in evening dresses and high heels and neither should you if you want to blend in. You don't have to wear a skirt to look feminine, you can wear jeans and a top and still be as feminine if you do it the right way.
Voice
Pitch. The female voice is of a higher pitch, about 225 Hz compared to 120 Hz, partly because women has different size chords and a smaller distance from chords to mouth. Women also have smaller throats than genetic men (in general).
Most genetic men have a spectrum that in the upper part can match the lower-middle part of a womans spectrum. This means that most men can, with practice, get a voice with a passable tone. This takes a lot of practice, thousands of hours, to master but singing lessons is a good start to get to know your own voice and learn to control it better.
Once the tone sounds well it takes some time in the mornings to warm your voice up and you may suffer from voice fatigue if you use your voice too much with too little practice. Needless to say is that smkoking will not help you in your pursuit for a female voice.
Social training. Women use words frequently that men only use occasionaly and the other way around. Men use more power words such as "We must do like this", "I have to leave" and "I need coffee" where women would probably use words like "Maybe we should do like this", "I should probably leave" and "I'd like some coffee".
A man usually emphasize the first word in a sentance and speaks with a tone that gets lower and lower towards the end of a sentance when a woman often varies her tone through the sentance and often has a tone that goes up at the end of the sentance, almost like when asking a question.
Women has a more elaborate way of describing things. A man would say "the house at the end of the road" when a woman might say "the BLUE house at the end of the road".
Women also speak with more rythm than men and pronounce vowels in a different way than men does. All of these social factors are important in understanding the difference between how men and women talk. Oh, and I almost forgot something, men speak to men in one way and to women in a different way. The same is true for women. Study, learn, practice. The way you talk and use body language is very important in order to pass. With a male vocabulary and a masculine way of talking that passable looks you have will end up to no use.
Body
Pose. You need move your body in a feminine way . Study how women act at the bar, how they drink, how they pull out a chair, open doors, where they keep their hands while walking or just standing in line, how fast they walk, how they hold their head, how they laugh, how they cry, how they sneeze and so on. Again, study real women, not models, and study women your own age.
Practice in front of the mirror... You can practice your voice to perfection but if you forget that you must also learn to sneeze, laugh and cough in a feminine way then it may be a giveaway and it isn't as easy as it sounds.
I am sure I could put in a few hundred lines more to this post but my goal was just to kill some time and not to write an essay.
Anyway, I think that if you actually read all this you realize that it takes a lot of hard work and thousands of hours of practicing by yourself followed by thousands and thousands of hours practicing this in real life experiences and hundreds and hundreds of faliures.
In the end and no matter how hard they try, not all transsexuals are blessed with genetics to pass and unfortunately there is not much to do about that. Even so I'd like to discourage people from undergoing facial pastic surgery before having seen all the effects from the hormones. Hormones have effects even after about 4 years of use and I'd advice people to let them do their job before doing anything drastic....
Hope this was interesting to someone, I really don't know why I wrote it.
Love,
Hanna