Carnegie wrote, "be absorbed by your subject." Chances are, if you feel strongly about a subject, that passion will be conveyed to your audience. Imagine relaying to a friend or spouse some injustice you have suffered at the hand of discourteous driver or disgruntled boss. Apply this same enthusiam, passion and/or vehemence to the delivery of your chosen subject.
Speaking in front of a large group of people can be a nerve-wracking experience. However, Carnegie recommended that the way to overcome a fear of public speaking is to build confidence by getting in front of an audience as much as possible. Whenever you have the opportunity to speak in front of people, take it. Include as many of your friends and family as will listen. Have them provide you with honest, useful criticism that will help you improve.
Part of public speaking is building confidence and believing in what you're saying. After that you must trust and believe in your success. Visualize the speech as a success, with enthusiastic audience members clapping and being congratulatory. Guard against negativity. According to Carnegie, "If you believe you will fail, there is no hope for you. You will." Save time. Speak and believe in the best outcome. Let your bearing be, as Carnegie said, "modestly confident."