The World's Most Successful Leaders Share Their Best-Ever Career Advice

Never look back in regret—move on to the next thing. Branson's mother taught him that "a setback is never a bad experience, just a learning curve."

Balance work and play. Huffington's message for young people starting their career is to be mindful of burnout. In a LinkedIn article, Huffington said she wished she could tell her younger self, "Arianna, your performance will actually improve if you can commit to not only working hard but also unplugging, recharging, and renewing yourself."

Learn to embrace failure. The Harry Potter series author says failure is an important part of career development. "I don't think we talk about failure enough," she said on NBC's Today Show. "It would've really helped to have someone who had had a measure of success come say to me, 'You will fail. That's inevitable. It's what you do with it.'"

Don't delay starting your own business. The founder of WayMedia and star of Bravo's Start-Ups: Silicon Valley says to start your dream business now. "There are so many free online tools. Just start, and if you fail you can always go and get a normal job, but you will learn so much along the way it will be a great experience," she says. 

Learn to self-review. The fashion designer says her best advice to those starting their career is to be self-reflective and trust your gut. "In order to trust yourself, you have to have a relationship with yourself," she told The New York Times. "In order to have a relationship with yourself, you have to be hard on yourself, and not be delusional."

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