Personally, I feel you should just pick up little things from these courses/books/etc. Just enough to make you aware of your body language or something subconcious that may unintentionally offend some people.
Bottom line is, I feel you should just be yourself. That way, if you make it, you know that you're exactly what they're looking for.
You'd never forgive yourself if you were not yourself at the interview, listened to some bloke who claims to have chaired airline interviews, changed your behaviour to what the 'experts' consider to be the 'perfect candidate', and shock, horror, didn't get through. The person they were looking for may have been who you REALLY are.
Answer all questions as honestly as you can, this includes the personality tests they make you do in most airlines. Also do your homework, knowledge about the company shows keen interest.
Ultimately YOU are the one who wants that job, so be yourself, don't let Mr. 'I've-seen-it-all' tell you how to be at an interview. Most people play themselves better than they play any other character.
Good luck with the interviews when they come.