How do I not get left out at this party?

So I'm going to this bat mitzvah tonight and I'm not gonna basically anyone, that is, except for like, ONE person...I want to have a good time. I want to have fun and meet new people, but I'm not always the best at making friends, and at events like these i usually end up being the weird girl in the corner not doing anything. Plus, everyone is going to know eachother already because they all go to the same school.( except me, i have the joy of going to private school ) How should I act and what can I do to be noticed? Thanks