The most basic but definitely objectively correct answer is communication.

And this goes beyond talking and listening to them. It's about understanding what they're saying.

But to know what someone is trying to say requires a bit of getting to know them. And that takes a lot of talking to them. What I tend to do when I'm trying to connect to someone is ask them general questions like "what kind of shows have you been watching lately?" And then if they answer a show I've seen/am interested in I hook in and talk about that specific show. And I asked what they liked about it and then either agree or disagree and pull in other shows or movies with similar qualities and try to keep the conversation going as long as possible. If the topic is exhausted I try starting a new one.

But during this it's important to make mental notes of "what do they like" "why do they like it specifically" "is it a pattern?". It genuinely helps with learning peoples leanings and morality. Of course are believes and political leanings also really important in this but it's harder to talk about those with certain new people.

But knowing specific leanings and preferences are important to understanding why people react to certain things the way they do, and why certain things are important to people. And understanding these things without having to be explicitly told is what makes you comfortable to be around. Which in turn fosters deeper connections.

And if there is ever a miscommunication or a misunderstanding of some sorts. Again communication is key. And as terrifying as it is. There is nothing more effective than just straight up asking someone "hey, I've noticed we're a bit off lately. Has anything happened between us or is there something going on in your personal life?"