Legendary investor and businessman Warren Buffett used to be so terrified of public speaking, he would become physically ill before taking the podium.
"You can't believe what I was like if I had to give a talk," Buffett recalls in the biography, "The Snowball: Warren Buffett and the Business of Life." "I would throw up."
But the young investor was determined to get over his crippling fear of public speaking and to woo Susan Thompson, whom Buffett would later marry.
So at 19, he enrolled in a public speaking course taught at Dale Carnegie, the institute named for the influential speaker and author of "How to Win Friends and Influence People" and other bestsellers.
After taking the course, Buffett was confident enough to speak in public and, perhaps more importantly, propose to Susan.
Today, would-be orators can hone their skills in the same class where Buffett developed his.
CNBC sat down with Joe Hart, president and CEO of Dale Carnegie, to discuss some of the most important lessons professionals can use to become better communicators — the same ones that that changed Buffett's life.
1. Learn as much as you can
"One of the traits that is awesome about [Buffett] is he is such an active learner," Hart tells CNBC. "It's something that's made him very successful."
Because Buffett is always learning, he's continuously building up the cache of topics on which he can speak auhtoritatively. And according to Carnegie, the best speeches are given by people who know a topic very well.
"Talk about something that you know and know that you know," Carnegie wrote. "Don't spend ten minutes or ten hours preparing a talk: Spend ten weeks or ten months. Better still, spend ten years."
2. Talk about your own experiences
Making a speech personal is the shortest route to winning people over, according to Carnegie.
"Carry a sheet of paper with you for a few weeks and write down, as you think of them, all the subjects that you are prepared to talk about through experience," Carnegie suggested.
These topics can include a big regret you have, your biggest ambition, or why you liked or disliked school.
3. Jot down notes, not a draft
If you watch Buffett speak, you'll see that he rarely looks at a piece of paper, if ever. That's because one of Carnegie's core principles is that a good speech is never typed up beforehand.
Instead, Carnegie recommended referring to brief notes, rather than reading from a transcript that can keep you from being present.
"When you stand up to talk, you will probably find yourself trying to remember what you wrote," he wrote. "That will keep you from speaking naturally and with sparkle."
4. Get excited about the topic
Smiling, having "positive energy" and exuding confidence make a huge difference, Hart says.
Buffett became passionate about investing, money and achieving success at a young age. That enduring enthusiasm comes through in his speeches and interviews.
As Carnegie put it, "Even people with only mediocre speaking ability may make superb talks if they will speak about something that has deeply stirred them."
Check out how Warren Buffett's reading routine could make you smarter and more productive
Video and additional reporting by Mary Stevens.