How do you deliver a speech if you're on live television. For starters, you're better off just ignoring the camera. If you have a large audience you need to be focusing on your audience, and you need to realize it's going to look weird if there's a shot over here showing you ignoring the audience and you're just staring at a camera. So, don't do that. Focus on your audience, and that's going to make things much, much better. Don't just pander to the camera.
The next thing you've got to realize is, that even though there's somebody in the audience who can barely see you, that camera can zoom in. Plus, you've got a microphone on. So, the tendency is, AND YES MY FELLOW AMERICANS THAT'S WHY THIS ELECTION IS THE PIVOTAL ELECTION. The tendency is to really raise your voice, to yell, to come across as extreme. If you do that the person 500 feet away may think you're powerful and charismatic, but on TV you could look like a lunatic. You could look too hot, too extreme, and it can seem like you're yelling. You don't want to seem like you're yelling.
Now, occasionally, to speak a little bit louder can be a good thing as long as you couple it with speaking a little softer. Variety is key. You want to be conversational. That's the biggest difference between the way politicians in the 1930's, 1940's, and 1950's spoke versus when Ronald Reagan came on the scene in 1980. He realized that TV changed everything for live speeches. You have to be personal and intimate, because your larger audience is not the people in the room. It's the people watching you on TV. So, you have to have that conversational quality.
Do that, and your speech will be a hit with the audience in front of you and the ones watching at home.