"Make eye contact", "shake hands" and so forth are that advice. However, since this is what you read, the piece you should pay attention to is "get a mentor." Until you do that, it appears you won't recognize the other bits of advice, which is one major reason to do so.
And that stuff actually works. I started out in life as someone on the borders of what would now be called an "autism spectrum disorder" -- I didn't "get" people, had trouble recognising them and distinguishing faces, and certainly couldn't make anything like a strong connection. When I was young, learning everything there was to learn about stuff was a decent substitute for life. Luckily (and here I use a meaning of that word that may be unfamiliar to most) I went through a grossly self-destructive phase involving poorly-planned and unreproducible chemistry experiments (even if you make the world suit your needs, you can make it go away for a while). The upshot of that phase was that I had to learn to be human as an adult after a period of being something completely other (the details of that period are beyond the scope of this discussion).
It took longer than I wanted, but I was able to learn to read faces, to associate body language and vocal modulations with various degrees and states of distress and "happiness" in others, making finer distinctions as time progressed, and after years of practice I found that I was no longer approaching the exercise from the viewpoint of clinical (but interested) anthropology -- the process had been internalised to the point where it was indistinguishable from empathy. What's more, I seemed to actually care, and my own emotional spectrum seemed to have more colours than "this sux" and "this rulez". It may be nothing more than an elaborate simulation running just below the horizon of observability, but it'll do nicely.
These days I'm not so good at technical matters -- a couple of strokes and the effects of Lewy Body Dementia have effectively removed me from that realm, though I still come to places like this to slow the rot -- but I've become the go-to guy for emotional support for a surprisingly large number of people who are emulating liking me in a very convincing fashion. And I'm emulating being happy with that, and can't tell it from the real thing.
