If you know the subject, it should flow naturally in most cases. Likewise, the best talks keep PowerPoint slides to a minimum. Don’t rely on anything more technologically advanced than text, and in particular, don’t try to link to the internet. The best thing to do is keep things light-hearted.
Then it’s just a case of coping with last-minute nerves. Turn up early to meet the session chair and get used to your surroundings. Have water to hand to cure a dry mouth, or to use as a prop when a pause is needed. Take your time but do be aware of the card-waving person in the front row (‘five minutes’, ‘please, please stop talking’, etc.). Ignore these only if the conclusion of your paper depends on them. And whatever you do, resist the temptation to applaud yourself afterward.