Practice "aggressive friendship". People love being invited to things so when you find someone you like, start asking them out. Play tennis. See a movie. Get coffee. Happy hour after work. Walk through the park. Get lunch at work. Be respectful, be ok with a no, but believe that you are worth spending time with. And count on the fact that most folks are lonely too, and will jump at the opportunity to hang, an opportunity you are now providing.

The other thing I'll say is that I feel very lucky to have made friends with people who were already part of a big friend group. It's hard to build your own community from scratch, it is much easier to join an existing one. Birthday parties, shows, cook outs, are group events and making friends with friends of your friends builds out your web.

It's hard work, I was pretty lonely for the first two years after I moved out to the bay knowing no one, but building relationships is one of the most rewarding uses of time I know.

This x 100. In many ways making friends as an adult is like romantic dating, but should be less stressful and easier. You just have to start asking people to do things together. You'll find that you really connect with some people, and others you won't but don't despair. Just keep "dating" until you find a group of people you enjoy hanging out with and who enjoy having you around.

My introverted ass spends at least 6 hours a year for the last decade wondering if I should install a Customer Relationship Management program to use on my friends.

I mirror other people, always have. If they are happy to see me, I'm happy to see them. But if they don't call, I don't call. If we are both introverts we collectively decide that the other person thinks we're a toad and nobody likes us. If it weren't for the "Extrovert who collects introverts" trope I'd probably have no friends at all (or at least, prior to volunteering). There are a bunch of people I only ever see when we both show up at a third person's house or event.