Just be friendly and approachable!
There will be many awkward silences which is to be expected; you put a group of strangers into a room together, there is always going to be uncomfortable silences and stuff. But don't worry about that, just say what you're thinking if you think of something funny to break the ice. Don't worry about what other people will think as they're more likely going to talk back or laugh because they're feeling just as insecure.
Just don't be one of those people who never say anything. Honestly, people do pick up on those things.
But groups shift all the time in the first few weeks of college, so don't think that everything you do now will affect you in a years time. A lot of the people just hang out with others just so they have someone to sit with at lunch, but as they/you become more confident and find out the personalities of other people you'll end up just finding a group that you feel comfortable with.
But speak up and let your voice be heard. If you don't understand something that the teacher is saying, then ask them to explain because the chances are is that everyone else doesn't understand either but is afraid to ask.