An emcee sets the tone for a particular event. She determines the energy level throughout and is responsible for keeping on schedule and establishes the kind of feeling the event organizers want.
An emcee has to have a pleasant stage presence, who is gracious, personable and flexible, who can think on their feet, keep many balls in the air at the same time, not get easily flustered, and calmly handle the unexpected.
She must knows how to set the appropriate tone for the specific session, carefully manage the time while maintaining a positive energy flow throughout the entire session, and who can make audiences/guests feel welcomed, special, comfortable and respected.
An emcee must be willing to put the time and effort into preparing succinct and willing to take instructions from organizers/clients too.