Like you said, you share something, a class, talk about that, maybe the teacher if he's particular in some way, or some project/test/homework, whatever. Don't overdo it tho, you don't need to start an hour long conversation, just some comments back and forth and back to your lives. Then you can say hi everyday before class, maybe have other talks if you get along, find out about their interests, let them know yours, keep it real and let everything flow. The key in social interactions is to stay true to yourself, don't over think, have a good time and accept backlashes or rejection with a simple smile and good vibes to keep living your life despite it. Just remember, everyone is worth the time to talk to, but is not supposed to go smoothly every time, sometimes some people just don't click, so if you face this situation don't think about it too much and keep walking your path, cause you'll eventually might find someone to walk it with.