Try to find out something about her--such as a hobby. Ask her questions about her hobby and use this as an ice breaker. Make sure you are sincerely interested in what she is saying--this will go a long way.
Do you know of something that the two of you have in common? Even if this something is very simple like having the same class together, you can use this as an ice breaker to start talking with this girl. Being a good listener and being able to hold your own in a conversation can go along way with girls.