For my job I have to do them alot. My wife thinks its hilarious cuz she calls me the most anti-social social being she has ever met. I hate people, yet I interact very well with them, especially during a talk.
The thing I learned is practice and never memorize. You have a general outline of the talk and getting the timing down. If possible practice in front of people to get feedback.
I used to be a big fan of Les Brown, because dude is just so smooth on stage. I finally met him and chopped it up and it blew my mind how much he prepares for his talks. On some lebron preparing for the season shyt. Blew my mind because the goal of practicing is so you can appear like you coming up with this stuff on the spot.