What are the most revealing aspects of one of the characters (consider thoughts, words, actions, descriptions, etc.)?

  One of the most aspects about my character is his strange mood swing's about certain people.Sometime's he changes his mood really fast,from happy to sad,to calm to mad.He also seems to talk to himself alot,but about the basketball move's he does.He says the tricks he does in his head over and over.I guess the only way he remeber's is to say them.Another interesting thing he does is go along and play by himself,he says thats the only way to get some real practice done.