I hope that you have never whistled at a girl or tried to gain her attention through a pickup line.
If you have you probably realize now that girls do not respond positively to these pathetic attempts to communicate with them. If you have not realized it and have gotten a positive response with this approach I suggest a visit to the doctor because you may be in need of some Penicillin.
During your actual conversation with a woman is when she will decide if you are a creep and mace you in the face or you are attractive guy and give you her phone number.
The best piece of advice I have been given on conversation is "You have to be interested in order to be interesting." In other words you must take the initiative to get to know her, this is done by asking her questions.
There are two basic questions I suggest:
1. Where are you from?
2. What do you do for work/school?
This will get a response for example: "I am from here, born and raised"
You should respond with a follow up question such as: "Really, so all your family lives here also?"
The purpose for these specific questions is they will almost always elicit a response that will give you more information for follow up questions.
Another example if you use question #2 and she responds with: "I work in sales"
You could then follow up with "What sort of sales?" or "How long have you been doing it?" or even simple questions such as "do you like it?".
After you ask 2 or 3 follow up questions you should answer the questions you asked her, regardless of if she asks them of you or not. In other words after she told you where she was from, and how long she lived there, ... you would respond with telling her where you are from and how long you have lived there.
By answering your own questions you accomplish two large obstacles.
1. She does not feel like she is being interviewed
2. She feels like she is getting to know you because you are revealing information about yourself.
Last tip; Don't say anything negative. Instead say good things and don't talk bad about other people. A woman will form a negative opinion of you if you are complaining about something or bad mouthing someone the first time she meets you.