Body language affects how others see us, but it may also change how we see ourselves. Social psychologist Amy Cuddy argues that "power posing" -- standing in a posture of confidence, even when we don't feel confident -- can boost feelings of confidence, and might have an impact on our chances for success.
(Note: Some of the findings presented in this talk have been referenced in an ongoing debate among social scientists about robustness and reproducibility. Read Amy Cuddy's response here: http://ideas.ted.com/inside-the-debat...)
I strongly recommend you read her book. Here's a link PRESENCE - BringingYour Boldest Self To Your Biggest Challenges