Girly Girl???.. Piss and Moan all the time about the littlest thing that happens that you don't approve of, wear the latest fashion trend at all times, and be stuck up and don't pay any attention to the normal people around you... or at least that is what my daughter complains about why she doesn't like girly girls.
But if you are meaning 'be more feminine'.. put on some make-up, care about how your hair is styled, and wear a little more feminine clothing.. IE: boys clothing is not feminine, no more comfy hoodies, and baggy pants...K?
My daughter is "developing" and is wearing all of the baggy hoodies that are so popular right now, because she is not used to her new curves, and doesn't really want the boys to notice that she IS getting curves.
She wants to be more feminine, and is experimenting with makeup, but still doesn't like dresses at all.. which is fine, but can become a comfort habit that later you aren't even aware you are doing.
I was a tom-boy when I was younger, but I was also the "tough-chic", and if I wore things that were too feminine, I felt out of place. Never the less, I began wearing jean skirts that were comfortable for me in texture, and still more feminine than just blue jeans, subtle changes like that were more comfortable for me. Instead of a ponytail, I started trying to curl into a style (which is really hard on your hair).. and I used so many aerosol cans of hairspray that I stand up now and take responsibility for personally damaging the o-zone!
You don't have to do much to be more feminine, a little makeup.. and not alot.. it looks gaudy.. goes a long way, a nice outfit "that you are comfortable in", will help, it's not how good the curves look in the clothes, it's how good you feel in the clothes, that will give you an extra boost of confidence and make you walk differently, and people will notice.