A good comedian is a person has good social skills. He has to know how to make people laugh through his jokes. Some of good comedians include Russell Peters, Mike Ward, and Jerry Seinfeld among others. Get information on how to become a good comedian on http://www.wikihow.com/Be-a-Good-Comedian.
John Valby aka "Dr. Dirty" ... he doesn't "tell" jokes, he SINGS THEM! He takes a song you would know and changes the words, i can't repeat it here though, I'll get deleted haha check him out on YouTube! :-)