Lol depends. if its a girl you know just be honest ha-ha tell her how good she looks and what you like about her. With the responses/expression she shows you can tell off the bat if she is into you or not. Dont give up if she is not interested, you can always change that ;). If it is a stranger you need to try to approach her in a way that is enlightening. Maybe say something that will make her laugh, smile, giggle, anything good. What not to do: Don't be an ass and try to look cool in front of friends. Don't try to say something like "Hey Girl, can i get those digits." They will most likely keep walking, say they got a boyfriend, or even worse curse you out or something. For beginners: Once you succeed in the first few steps and feel like the conversation is coming to an end, you ask for her info (#, Fb,Insta,W/e). Ex: "Oh hey it was really nice meeting you and talking with you. Do you mind if i take your number down? you seem like an amazing person to talk to." Ps: Keep Eye Contact. Smile. Be happy. (Hope this helps.)