These 'self-improvement' gimmicks are a kind of tax on people newly intent on improving themselves. They are beneath the dignity of a true hacker.

If you try to mess with your body language you'll just look creepy. I suppose an exception to this is if the person you're trying to impress is sufficiently dumb and insensitive as to not notice. In which case why bother trying to impress him?

Instead of trying to project the image of a confident, kind person, try being a confident, kind person. The body language will follow naturally.