Let's take a look at the former US President Bill Clinton. There is no denying that he is one of the most gifted communicators in the world. There are many reasons why Mr. Clinton is so effective in speeches. Some of the characteristics that make him so successful are his confidence, his appealing, human style presentation of plain logic and support, and his evident storytelling skills such as providing obvious examples and drawing pictures with his words. I am not suggesting you be Bill Clinton, but that you speak in a "human voice."
In other words, be here now. Be aware of your breath. Be aware of the audience. If you're thinking about your nervousness, or what you're going to say next, you are not truly present. Your "presence" is your present to the audience. Be real, experience the moment, and allow yourself to go off message if the moment presents itself. Be here now.