Don't underestimate the power of body language. I don't recall the exact breakdown, but more than 50% of communicatoin is through body language. Charismatic people often share certain body language, including walking tall and with spine straight and using open gestures (not folding arms/legs, etc). For most people, their body language reflects how they're feeling inside, but your feelings and your body language are very closely tied. That means that if you adopt a closed poster (legs crossed, back bent and arms crossed), you'll start feeling more closed. An open, strong posture can make you feel better and more confident.