How to approach girls in my classes?

College pickup is not really talked about a lot here, and it is said you build a reputation if you do direct approaches.

I go to a relatively small college, and most people in my program know each other. How do I approach girls in my class without making a reputation?

Also, most of them have their own social circles and tend to stick to them. People are always in groups and make it hard to approach them. How do I go about doing this?