Mindy Kaling didn't get her start in Hollywood by leaning on connections.

Instead, she landed writing jobs, and then launched her own shows by doing three simple things, the "The Sex Lives of College Girls" creator said in her new course on MasterClass.

"My success didn't happen exactly how I planned it, but the failures and obstacles along the way actually created different opportunities," Kaling said. "Doing the hard work, having confidence, and being ultra-prepared will set you up for your success."

Those three traits were particularly important early in Kaling's career when she had to hustle to be noticed. After being hired as a staff writer on NBC's "The Office," she made sure she arrived early, left late and confidently knew her notes on every character and scene.

When it was time to start pitching her own shows, she'd practice the material three times before she had to present her ideas.

By putting in the hours, both physically at work and mentally on the material, Kaling had the assuredness to pitch ideas in settings where the others knew each other and had more experience than she did. "I never had a moment of being like, 'I shouldn't be here,' which is strange," she recalled with a laugh.

"If you can approximate that or fake that [feeling], I think is very useful," Kaling said, noting that "sheer will" and a lack of impostor syndrome helped her career.

'Confidence is serious business, and the single most important differentiator in the workplace'

Confidence is an effective strategy to climb any career ladder, according to some leadership experts. It's a strength, for bosses and employees alike, because it's the key to making "very impactful decisions," says Bonnie Low-Kramen, author of "Staff Matters: People-Focus Solutions for the Ultimate New Workplace."

"Confidence is serious business, and the single most important differentiator in the workplace," Low-Kramen wrote. "It will be the person with high confidence and lower abilities who will get the job over the person with low confidence and higher abilities."

For Kaling, it seems preparedness, hard work and confidence have become almost synonymous. Most of her scripts wind up in drawers instead of on TV screens, but she has the self-assuredness to know she can withstand rejection and rebound with new ideas, she said in the class.

"I've never had any [innate] confidence," Kaling said at the Glamour Women of the Year Summit in 2018. "I've just done the leg work. It often meant that I never came to anything unprepared."

"I literally couldn't not be confident with the amount of research and preparation that I had done," she added. "I think that's sort of been the key to everything in my life."

Want to make extra money outside of your day job? Sign up for CNBC's online course How to Earn Passive Income Online to learn about common passive income streams, tips to get started and real-life success stories.

Plus, sign up for CNBC Make It's newsletter to get tips and tricks for success at work, with money and in life.