How do you talk to a girl and become friends with her if she is always with her friends?

[Tom]

The best time to get to know a girl is when they're alone, this way they aren't pressured or embarrassed, this makes it easier for them to be themselves and gives you a better chance of getting to know her as she will be more open to conversation.

If you never get the chance; add her on Facebook or any other social network you two are on and chat there, get her number etc.