Join something. Anything. The way that you make your best friends (at least in my experience) is by seeking out people who are interested in similar things. You can become a member of a new club or take a class in something you've always wanted to learn more about; it's all the better if it is not something you would normally try!
Take on a new challenge. If you've always wanted to perform but have been too afraid to audition, just do it! Pluck up your courage and try out for something that scares you. It is only through challenging yourself that you can grow.
What do you do to put yourself out there? Have you ever tried any of these methods?