There are a lot of posts and articles about how autistic people make friends or how to improve the ability of autistic people to make friends, but I think they may be missing the mark.
I'll admit, even with the article I wrote on the subject (linked above), I offered my own "formula" for how to make friends, but it involves a lot of masking and social scripting. It wasn't something I was taught; I just sort of taught myself.
When I say "miss the mark", I mean I think there's way too much focus on helping autistic people make friends by trying to change the autistic person's behavior to make them appear more neurotypical.
Making an autistic person behave in a more neurotypical way will always backfire. We don't have the same set of social skills, intentions, or motivations as neurotypical people. That isn't to say one way of interacting is better than the other, but they don't match, and both neurotypes can seriously misunderstand each other if they don't realize they are speaking two different neurological languages.
This is why it's hard for autistic people to make friends. We're in the minority, so, by default, we look like "the weirdos", the one making mistake after social mistake, and it's seen as something done on purpose or because we are somehow dangerous.
How do you (or your autistic loved one) make friends? Are you more likely to be friends with people who are also on the spectrum? Do you make friends through trial and error? Do you prefer your own company or the company of animals instead?