Ok, we all need to practice, train our respiration and voice intonation. There's a lot of tips about it. But one of the most important thing is to present a clear message.

I liked the book "Made to Stick" http://heathbrothers.com/books/made-to-stick/ about how to clearly present your message. They have a very good summary designed for presentations called "Making Presentations That Stick". The authors will give it in exchange of subscribing for their mailing list: http://heathbrothers.com/resources/overview/ (it is in the bottom of the page)