I'm 25 so my experience is a little easier since people my age are looking for friends more actively, but I still think I can provide some advice. I have a huge friend group that I'm very proud of and put a lot of work into developing.

1. You have to meet potential friends in the first place. Bars, clubs, bookstores, community events, volunteering, neighbors, etc. Ask about people's interests and hobbies and see if any line up. Maybe you both like horror movies or a certain video game or something like that.
2. You have to be active about it. Invite people to things, and put effort into it. What you do is up to you, but some universal things are dinner, board games, movies, etc. Don't get too nervous about if it will be "boring" or "cool". The way I think of it, is would I rather have a boring time with my friends or be on my phone by myself? I chose boring time with friends every time.
3. Don't be afraid to give up on making a certain friend. If someone isn't being responsive or doesn't seem interested in hanging out, that's totally fine. Just move on. Don't dwell on it. When I first moved to the city I live in, I tried making something like 15 or so friends and only about 3 of them actually went through with plans, and now we're all besties. That means only 20%. Like I said, you have to put in effort.