Ordinary speakers merely convey information, and have no stage presence. They remind us of Shakespeare's immortal lines in Macbeth:
Life's but a walking shadow, a poor player
Who struts and frets his hour upon the stage
And then is heard no more. It is a tale
Told by an idiot, full of sound and fury,
You don't want to be a walking shadow, do you? You are looking forward to a career as a successful public speaker, not someone who merely 'struts and frets his hour upon the stage', and when they go away the audience forgets about him immediately. You want to be an impressive speaker, whose words find a resonance in the listeners' hearts and minds, and stay with them long after the speech has ended. You want to be one of those who can charm and captivate those whom they speak to, and hold them spellbound for hours together, make them forget other concerns for the duration of the speech, and carry utter conviction with force and clarity. How can you become a speaker like that?
There was a special branch of study in the ancient civilizations of Greece and Rome which dealt with precisely this problem. As you perhaps know, many of the ancient city-states were democratic in nature, and their form of democracy was much more direct than what we can have in the modern world. Being small (by today's standards) habitations of a few thousand people, they were able to practice direct democracy, which means that the people were able to influence the government's policies directly, without there being any need for local representatives.
Those who wanted to be elected to the government, or to influence public opinion for a political purpose, had to be well versed in the art of public speaking, because they had to convince the people through open speeches delivered at a central clearing in the city, called the 'agora'. This branch of learning was known as 'rhetorics', and it was a very important part of a young man's (for women did not take part in politics in those days) education if he had any sort of ambition for high office.
Even today you shall see heads of state or presidential candidates or members of a parliament debating each other on TV or some other forum. They are just following an ancient tradition that started thousands of years ago. But in today's politics convincing the public isn't really the most important thing, specially after the elections are over. There are other ways of gaining and holding on to power. So the study of rhetoric has become relatively unimportant.
So what can you do to become a good speaker, like the ancient politicians? Well, one of the first things you need to learn is not to speak impersonally. If you stare above the head of the audience and address your speech to the ceiling or the open space, you shall fail to engage your audience. So from the very start, look them in the eyes directly. Select a few faces among the masses and speak personally to them.
Use a friendly tone, and don't appear superior or nonchalant. It is good to have an attitude, but too much of it can make the audience reject you as just another smart guy. So carry yourself with style, but still be humble. By no means should you give them the feeling that you're much above them. It is this balance between self-respect and humility that will most often carry the day for you.