Found on r/AskReddit. Thanks to all that gave permission to republish.
1. Make friends by being friendly. Go out to bars. Join clubs of things that interest you. Go to work functions.
I would try to find a hobby or club and invest in it. That way you’re making friends that have similar interests. Also don’t judge people automatically. This will cripple your chances.
2. Hang out with work people outside of work and with their friends. My friends increase through mutual friends. a lot of the time I end up leaving the job and years later I’m still friends with that person I never worked with but met through a co-worker.
Conventions are also a good place to make friends.
3. I started commenting on a blog about my favorite pro sports team. We all started getting together and I found a ton more friends from that.