One of the biggest mistakes I see presenters make during public speaking engagements has to do with the handling of question-and-answer sessions. The presenter does a good program, has a powerful close, opens the program up to questions, answers them well, and then fades off the stage into oblivion.
The lack of a second powerful close after the question and answer period could negate much of the impact that was created throughout the program. Make sure you have two good closes whenever there is a possibility of a Q & A session.
Trick: Purposely omit material that you know will evoke certain questions. When the questions come, give a preplanned answer that appears spontaneous. They'll think you are a genius.