People with great presentation skills know that a large part of engaging the audience is simply being you. For some reason many people think that once you get up to speak, you’ve got to take on an entirely new persona. You have to be an entirely different person at the front of the room, because you’re speaking to a group.
The more spontaneous you can be, the less “practiced” you seem, the more likely you will come across as the genuine person you are and the more impact you will have on your audience.
Most people don’t feel uncomfortable talking one-on-one. Similarly, when you have a discussion with somebody about what’s going on at work, you don’t prepare for it for three or four hours ahead of time or with a written down set of points, and a practiced set of words. Typically so long as you are passionate and knowledgeable about a subject you’ll have plenty to say