- co workers
- when I moved cross country, I had a few friends in dc already, started hanging with their friends and stole some
- joined my alumni club
- made two friends off of Craigslist
- join clubs, activities, meet ups - professional clubs, rec activities, the gym (if you go to a smaller independent facility - I've made good friends at my gym), poker club, frat/sorority, civic engagement, family dinner, book club etc
- ask people if they know people in the city you're moving to and have them connect you
- hitting up the bar alone, pretty much every time I sit in the bar area of a restaurant alone I meet someone, about 1/4 of those could actually become acquaintances if I cared to make it that
Edit: neighbors, especially if you live in a big apartment complex
You probably won't find new BFF's as an adult, but it's pretty easy to find people you can at least count on to hang with or do social things together.