How do you make it so you don’t feel left out in a group?

I take it this is in the context of group-work in college? Well that sounds a bit like working professionally with others in the work-place. After introducing yourself just a little, not too personal but things mostly relevant to the task at hand, you then keep most of the interaction relative to the work. As trust builds gradually, your work-based interactions will gradually show you who you'd like to know better and who you wouldn't. Then you could gradually start opening-up personally with the people you like, maintaining professional boundaries so that the work still gets done. Just my thoughts :)