The 7 best side hustles to start that will earn you 6 figures or more, and how to get them off the ground quickly from experts who have done it

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Apple was Steve Job's side hustle.

• As you enter the new year, you might want to turn your side hustle into a high-paying career.
• Some of the most recognizable companies like Apple, Twitter, and Facebook started off as side projects and later became multi-million dollar corporations.
• Business Insider talked to entrepreneurial leaders who earn six figures or more with their side hustles, and we've gathered career advice for those who are looking to bootstrap their businesses.
• While Joana Galvao, founder and CEO of Gif Design Studios, recommends old-fashioned networking approaches for freelance graphics designers, influencer Huda Kattan suggests getting the legal paperwork done as soon as you can.
• Click here for more BI Prime stories.

As you enter 2020, you may take on a side job for a number of reasons. Whether you're doing it to pay off your student loans or to pursue an unfulfilled passion and eventually become your own boss, you may be able to turn your side hustle into a high-paying career.

In fact, some of the most recognizable companies like Apple, Twitter, and Facebook started off as side projects and later became multi-million dollar corporations.

That is the art of the side hustle: You get to give entrepreneurship a test-drive all while earning on your own terms. Better yet, what you work on in your spare time may just be a billion-dollar idea.

Given the time constraints that come with working on a side job in addition to your main career, side hustlers have to master the key entrepreneurial skills of efficiency and productivity, accessing the learning tools and tweaking simple income habits.

Business Insider talked to entrepreneurial leaders who earn six figures or more at their gigs about their advice on building side hustles.