I don't think that there is any one specific way that all charismatic people behave. Two people can behave very differently and be charismatic in their own ways. Napoleon Hill in his book Think and Grow Rich suggests spending 30 minutes a day just envisioning the person you want to become. You could picture yourself charismatic and confident. Don't underestimate the power of your mind! It's capable of a lot and we really have no way of explaining it... its fascinating.