[tdfx]

If you're not naturally social you should involve yourself in some activity that forces interaction with other people. Consider a weekend job at a bar or popular night spot. If that's not your thing, try finding groups on Meetup that involves interests you like/might be interested in. Maybe even pick a few outside your comfort zone.

Very few people have the kind of personality that allows them to naturally develop friendships with the type of people they prefer to be around. Given that, it's basically up to you to find activities/work/etc that puts you in "social proximity" with the kind of people you want to have in your life.