I generally agree with the comments others have made about not using magic to flirt with girls. On the other hand, if you are going to approach a girl on the street (or anywhere else) to do magic for her, it is worth considering what kind of magic is likely to please her? Most women (and I am generalizing here), but I think most women like flowers and chocolate. I don't do street magic, but I frequently perform in restaurants and at special events. I often carry small, artificial, but pretty looking, roses with me - the kind you can get in arts and crafts stores, and I walk up with the rose palmed in my hand and between my first and second finger. I have a piece of flash paper gripped between my thumb and first finger and a lighter in the other hand. I light the flash paper, produce the rose out of the flames and present it to the woman. It is a stunning trick, an opportunity to give a gift, and usually very well received. You can also produce a Hershey Kiss (or more than one) in this manner. If there is a couple by themselves, for example a girl with her husband or boyfriend, I often avoid doing this kind of trick because I do not want to make the male jealous or resentful, or to show him up.
With males, I often walk up and produce an old silver dollar out of the flames and then do some sleight of hand with the coin. These techniques avoid the awkwardness of approaching strangers, telling them you are a magician and asking if they want to see magic. After all, with the above-mentioned techniques you have already done magic and established your self as a magician. More often than not (but certainly not always) they will want to see more. But even if they don't, you have already performed for them, and have probably entertained them.