… Do it; suck. Do it more; suck less.
“How to Make Friends and Influence People” is a great & classic book about giving people social room, focus, support, and attention with genuineness and humour (“influence” isn’t meant in a manipulative sense). Effort and attention are required, and practice, but that’s the cost of change and improvement.
“How to Make Friends and Influence People” is a salesman's guide, Dale Carnegie was an traveling salesman and the book techniques he learned making sales. The techniques you need to be a salesperson is probably not the same techniques to build lasting relationships. These tips are great for brief interactions; they are not for building relationships.
There's a couple of things that need serious caveats -
The "using the person's name" is so well known it's now clocked as exclusively a sleezy sales behavior. Don't do this - you sound like a sleezy salesman.
Asking people endless questions about themselves can really come off as a really weird integration and can be extremely off-putting if not done carefully/correctly and with grace. My mom does this, she asks hundreds of the dumbest most inane questions and she doesn't even listen to the answers to. It's so insufferable that people actively avoid her. I'm sure she read this book and thinks she's a social genius.
https://www.buzzsprout.com/2040953/episodes/17943742-how-to-...
"And also, if you think about these tips of smile and try to avoid arguments and greet somebody enthusiastically a lot of these are tips for making somebody like you immediately... They're not tips for ongoing relationships. They're like, when you show up at somebody's door, how can you make a good impression in the first five minutes and establish trust very quickly?"
Most friendships are made by doing something that puts you in proximity to the same people repeatedly. Go join (or start) a pickup sports team. Or a reading club. Or a run club. Or hang out at a bar on the same evening each week. Find something that aligns with your interests. Do it with other people. If they invite you to grab dinner or go somewhere afterwards, go along and keep talking.
The goal isn't to interview people.
If you're into music, find out what local/regional bands are in your area and where the small local venues are. Show up a little early and talk to strangers.
Rock climbing isn't for me, but my brother has made a bunch of friends at the local rock climbing gym.
Bird watching clubs are everywhere and you guys can nerd out over different camera setups.
Join a running or cycling club. I've heard the ones around here are very welcoming to people new to the sports.
Table top RPGs are fun. Your local game stores probably have one shot nights where everyone is welcome and noobs are encouraged.
Find some sort of hobby you enjoy and find others who want to nerd out over it
Make new friends with others that have underdeveloped social skills and figure it out together.
Do things in a group in some activity that won't put the spotlight directly on you and where you can observe others.
Explore therapy where odds of rejection are pretty low since you're paying them for coaching.
I think noticing how children play is very instructive, but if you don't have good social awareness that could get you in trouble. Kids haven't internalized all the baggage you and I might have about social rejection and awkwardness yet. They just confidently say "hey I like your bracelets will you tell me what they mean to you?" and if it doesn't pan out this time they play with someone else. It's the social anxiety / awkwardness that usually makes people the most uncomfortable, not the atypical interactions. Kids don't have that at all.
The one little girl is black and has very tightly curled hair. Every few weeks she has it done up differently, with different colored beads, etc. I make sure to pay attention to when it changes so that I can tell her that it looks amazing, and she gets a huge smile on her face every time. It's often the highlight of my morning, and I truly hope that she heads off to school with more spring in her step.
Adults aren't much different -- they also like to receive compliments. Give out compliments as you see fit and soon you'll have something in common to talk about.
If you're really hard up for social skills, and you like being around silly fun people and are okay acting silly yourself, I recommend taking an improv class. Any introductory improv class is basically kindergarten games to help you realize how low stakes socializing can be.
But I also realize improv isn't for everyone. In that case I recommend finding an activity you might be interested in and taking a class in it. If you aren't sure what you're interested in, good news! That means you get to take all the classes until you find one you like.
Even if there's no classes for your activity, anything that can be done out of the house and with other people probably has a community built around it. Use your interest in the activity as leverage to expose yourself to that community.
Spend some time on that website, see what you can dig up on specific skills, and then test using them in real life.
That site skews heavily towards therapists, and has a lot of woo-woo. It is clearly not THE answer.
But it is A answer. Enough to give you a framework to get started.