Find common interests, pursue your interests with people who are doing the same. Keep in touch with old friends that didn’t turn out to be shitty people, be friendly, go to social events and be friendly, take your common interest friends to social events and ask them to bring invite their other friends, ask coworkers to hangout, establish common ground with literally anyone anywhere, do it enough times you get good at it, establish common ground well enough and it is easy to keep people around, as long as you don’t suck – that may be the biggest part, be a goood person, be dependable, engage, don’t be shitty