Believe in yourself and apply maximum conviction and dedication to what you are doing. Don't "try", do it. This puts you ahead of the competition.
This applies to your physical body as well. If you are constantly slouched with a frown on your face and arms crossed, that may not serve you well. That kind of posture can come across as defensive, negative or closed minded. A strong, positive, and open posture will make things that much more attainable.