Successful side hustlers reveal 4 key steps for getting a new business off the ground in 3 months or less

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There are many moving parts to a side hustle.

• It's hard to know how to start building a side hustle, which is a freelance gig or a business idea that you pursue on the side while working a full-time job.
• Though there's no right or wrong way to start your side hustle, making smart decisions early on can make you more successful.
• Five experts shared with Business Insider hard lessons they learned that helped grow their side gigs.
• Longtime business coach Justine Clay recommended creating an excel sheet and setting quarterly goals for your side hustle.
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For some people, a side hustle is another way for you to earn more money on the side while working a full-time job. But for others, a side hustle is a career choice - an out-of-pocket investment of money and time to pursue original business ideas.

When done right, side hustles can be rewarding. You get to call your own shots and be your own boss. Better yet, what you work on in your spare time may just earn you six figures or more. What separates the high-earning side hustlers apart is their plan.

"There's a lot of advice out there that tells people to just do it, like jump on the parachute and hope for the best," said Justine Clay, a longtime business coach that specializes in helping entrepreneurs and freelancers. "But you've got to build it with intention rather than it coming from a place of desperation or panic. You need a plan."

Starting a side hustle can feel like you're jumping into the unknown because there's a lot of planning to do.

Given the time constraints that come with working a side job in addition to your main career, side hustlers have to quickly master the key entrepreneurial skills of efficiency and productivity. They should also seek out tools for continuing education and tweak spending habits. You also have to set business aims and work out the logistics as soon to hit the ground running with your new career.

Five experts shared with Business Insider the decisions they made that grew their side hustles.