Amy Cuddy of has a great explanation from a social scientist's perspective how we are judged by our body language.
One thing that Harvard Business School has just learned what we have known in theatre for a long time. You can't separate the way you move from the way you think. It's the reason that "presentation skills" separated from the business proposition you're developing has much less impact when the two are done together.
Each influences the other, and both when developed together reinforces strengths and weaknesses of your case. Be careful of people who say there are tricks to presenting effectively. These are minor. The most important thing to know is that how you think, develop ideas, and present them must be a unified process.