Sit near her during class, like behind her or next to her. When you sit near her, you then open the door to a possible before-class conversation or talking with her when the professor asks the class to discuss a topic during class time.
Introduce yourself so she knows who you are. A simple get-to-know you conversation can lead to other
conversations. Ask her questions. You will be able to get to know what interests her by having a casual conversation.
Arrange for a group study and invite her to study with the group. This will give you an excuse to ask for her phone number and see her outside of class. By studying in a group, she won't feel as pressured as she would if you were suggesting a one-on-one study session.
Ask her out when her and you are by yourselves, away from your fellow classmates. Walk with her after class and ask her out then. Keep it casual. Remember to use any of her interests to ask her out with. For example, if she says she likes a certain band and there's a concert coming up, ask her if she would like to go with you to that concert.