Talk with sense.

Captivate people when you speak by not talking until you have something to say. Never talk because you want to say something. When you do, you end up repulsing your audience. Speak because you have something to say, and there is a compelling reason for you to do so. Never speak simply because you are expected to speak. When you do, you are reacting, not pro-acting. Follow this rule, and you will notice people start hanging on your words. That is the first sign that your words carry authority.