Charismatic people tend to have that thing that makes people enjoy being around them. Admittedly, not everyone is a social butterfly. There is a multitude of variables that can affect one's willingness and ability to be social, such as mood, time constraints, etc. At some point, however, it becomes crucial to set aside the excuses and obstacles, especially to rise to the ranks of the most in-demand musicians. Sometimes the simplest of things go the furthest, such as taking interest in someone else's conversations, making eye contact, occasionally going out of your way to help a colleague. More or less, be self-aware and always be thinking about how your actions are affecting others and impacting the atmosphere of the rehearsal, performance, etc.