When I gave a talk as a "Role Model" for 3 classes of 12yo girls at a careers-in-tech camp, my final advice boiled down to - if boys get more opportunities, it's because they act like they deserve them. Stand up straight, look people in the eye, act confident, and trust that even if you don't know, you can find out.

This advice is probably millenia old. Still good.

If you want to learn more, you might want to start with something like How to Win Friends & Influence People. It's old and cheesy but 100% accurate nonetheless (good history lesson too). It's always about the other person's experience, and not about you.

A great modern book is "The Hard Truth about Soft Skills."

There are several books on body language itself, but they typically don't have more information than the OP article, and then are filled with excessively speculative/suspiciously detailed interpretations of other things.

Perhaps the most important thing for hacker-types to learn is that your body language, attitude, behavior isn't about other people judging you - but you showing how you judge them by the effort you put into your appearance and attitude for them. You put effort into it == you respect them. It's just that simple.

The second most important thing to know is that there is no true way to detect if somebody is lying or insincere, and lots of those body language books argue that there is. Gut instincts are real, and when people lie they often believe what they are saying anyway, so you gotta listen to your gut and not try to analyze if their eyes looked up and to the left or their eyebrows quirked, or if they covered their mouth with their hand. While you're trying to micro-analyze this crap, you won't be paying attention.