42-year-old Amazon seller whose side hustle brings in $143,000 a month: Use these 3 simple steps to make more money
Jenny Woo's four streams of income have taught her a few important lessons: how to start side hustles, sustain them and make them more lucrative.

Woo is a 42-year-old ex-corporate consultant and Montessori school administrative director who lectures at the University of California, Irvine, runs an online emotional intelligence course and freelances as a business consultant.

She also has a side hustle called Mind Brain Emotion where creates emotional intelligence-focused card games — 11 of them so far, on topics ranging from relationship skills to job interviews — and sells them on Amazon. The games brought in $1.71 million in revenue last year, or an average of $142,700 per month, according to documents reviewed by CNBC Make It.

The side hustle's success is due, at least partially, to a three-step process Woo followed, she says: Keep testing your idea after you've launched it, use the feedback to inform your next project and repeat the cycle.

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Woo's first game was meant to help teachers and kids learn the basics of emotional intelligence, so she spent three months testing it in local schools before listing it on Amazon, she says. Once sales started coming in, she kept researching and testing the game — but instead of updating it, she used the feedback to create new versions for different topics and audiences.

"Iteration is key," says Woo. "For those who are risk-averse or perfectionistic, they may worry, 'What if I make a mistake? What if I become irrelevant?' Don't be afraid to reinvent yourself."