• Stop declining when people invite you to stuff.
• Stop being picky about activities/food/music/etc.
• Be vigilant/safe, yet open minded, open to new experiences, spontaneous.
• Plan trips and events, both budget friendly and splurgy, then actually commit to doing them.
• Smile and laugh n shit.
• Compliment people, thank people, be considerate to others even if it's not always reciprocated.
• When it is reciprocated, gravitate more towards that person, and gravitate slowly away from people who don't seem to appreciate you.

Hobby clubs, fitness groups, volunteering, specific interest events. Personally, I plan to attend more local events. There are some upcoming local events that pique my interests.

Search for a community of people with similar interests where you live. E.g. something you like doing for a hobby.

Volunteer

You can be social and go to events but that only helps you meet people, it doesn't mean you'll make friends. I've recently moved, first year I was completely alone because I thought that eventually someone would come up to me. Most people are like that. They're passive and expect friendship to pop out of thin air. I put together a basic strategy and now I have 2 friends I hang out with and a few acquaintances. Here it is, hope it helps.

• Most people are just as socially isolated as you. Lots of people are the passive partner who won't initiate but they still want to make more friends. Covid-19 fucked everything up so this is actually the best time to make new friends if you can approach people.
• Pick someone you're interested in and introduce yourself. It can be anyone and for any reason. My best friend of 10 years only became my friend because I sat next to him in 1st grade lunch. You don't need a reason to talk to someone. Talk to people you aren't interested just to get the feel for conversation, older folks work great as they're low risk and just happy to have a conversation.
• Talk to this person every time you see them. Basically, pretend you're already friends with this person. Ask them about their weekend, what their job is, and how they got into whatever it is you're at. Start with 2-3 minute small talk and gradually make your way to longer conversation.
• Repeat these interactions for about a month.
• If you like them, say you're going to see a movie or whatever other activity and ask if they'd like to join you. Invite them to something you're already doing, even if you'd only do it to invite them. It puts less pressure on both you and that person.
• If they say yes, you've pretty much made a friend. All you need to do is keep the inertia up by scheduling a recurring event. Best case scenario, they invite you to a bar group and now you can make more friends by proxy.
• If they say no, go to the event anyway and try to talk to someone. If it wasn't an outright refusal then you can try again. If they don't take the second invitation, pull back and focus on someone else. Put the ball in their court and see what happens.
• Repeat until you have friends.

A lot of the advice other posters give is great for meeting people. But it implies that you're already able to turn a meeting into a friend. You'll probably suck at it for the first 3 months as you flex your conversation muscles, don't worry about it. It's a long-term process and it will get easier. Oh and of course modify the advice to suit your situation.

Hobbies and pursuing them. Like board games? Join the local game night! Like sailing? Join a sailing club and attend! Like football? Join a local football team. Like thinking and debating? Join a Sceptic Society!

It’s hard to be the new kid, it never changes with age, but you just need a few shared experiences and people start thinking of you as part of the tribe.

My partner and I recently moved to an entirely new city. It’s in a region I’ve lived in before, but a different city.

We found a meet up group called “ 20 something’s meetup” and went to a few events. We found some people we really enjoyed and invited them to a few other events, and still regularly attend the group as a whole. The internet has done a lot of work for us.

Board game meetups and clubs work great

Join your local Marxist organization.

I started playing disk golf which has started to build up some sort of social network. Doing a physical activity with other people really seems to work.

I think we make too much of a deal about making friends as adults. Kids are so much easier in this: “Want to be my friend?”, “Sure!”
I’m guilty about this as well, too shy and awkward to just make friends. But I believe most people would be happy to have a new friend if the other made the first move. We’re all just so socially awkward about these things.

Anyway, if anyone wants a friend, I’ll be your friend :)

I realize this doesn’t really answer the question. Best way is to be open and eager to make friends, I suppose?

I saw a shirt sometime saying something like "At a certain age, you have to give birth to new friends." While it wasn't exactly like that, we made a lot of friends through our kids and their schoolmates or sports activities.

There’s tons of good comments here. Mine will echo some! I just wanted to share my experience.

I have three hobbies that I’ve explored since moving to a new city in my 30s - axe throwing, pinball, and making music.

I found a local axe league and joined for a season. One season has become four :) The people I throw axes with are wonderful and varied. While we may not have crossed paths otherwise, they’re fine folks and I consider many my friends.

I went to a local pinball bar for a casual tournament and have been going every other week since. It a supportive community and I’ve had a great time learning about the games and learning about the folks on my various teams.

I answered a Craigslist ad for a band looking for another member. We’ve clicked quite well and have practices together, go out together, record together, and even play shows!

Exploring your own hobbies in some sort of structured way might be a good step in your own quest :) Good luck!

It is simply impossible.

Volunteer. All the best people do.