Starting a passive income side hustle may look quick and easy on TikTok. In real life, it usually takes time and effort to start, and maintain, a business that brings in cash while you're actively not working.

"Don't put unnecessary pressure on yourself to create a six-figure business in two weeks," Jannese Torres, a 39-year-old blogger and podcaster who makes $9,300 per month in passive income, wrote for CNBC Make It last week. "That's not realistic, despite what social media may tell you."

So, what is realistic? Make It spoke with a group of experts who've built passive income businesses and scaled them into six-figure successes.

Here are their top four pieces of advice for starting and growing your own:

Use your past experience

Your side hustle's success can come down to how you apply your personal and professional strengths to your business. For JP Mancini II, a previous career in sales at a car dealership helped him build a successful boat-rental business, he told Make It last year.

It equipped him with some necessary customer service and marketing skills, and taught him the value of owning luxury products that could actually hold some resale value over time, he said. From January 2022 to January 2023, his two boats — one in Hampton, Virginia, and another in Key West, Florida — brought in more than $466,500 in revenue, according to documents reviewed by Make It.

It took time, and cash, to launch the side hustle: Mancini spent 300 hours researching what kind of boats to buy, and as of last year, was working to pay down $550,000 in debt from the boat purchases.

But the job came with rewards: Mancini only worked 30 minutes per day, which gives him more time to travel and enjoy time on the water, he said. He stood out on boat-rental platforms like Boatsetter and GetMyBoat because he knows how to craft a customer experience in the luxury sector, he added.

"I was born to be a salesperson," Mancini said. "When you really understand sales, you know there's only two reasons people buy things: to fix a problem, or because they love something. I think you have to understand the psychological aspect of why people spend an exorbitant amount of money [on anything]."

Set small goals — and gamify your process

Last year, web developer Ryan Hogue made more than $1,600 a day, or roughly $11,400 per week, largely in passive income, according to documents reviewed by Make It. But when he launched his first attempt at passive income — a print-on-demand business — in 2016, he only made $4 per day for his first couple of months, he told Make It last week.

Instead of getting hung up on the dollar figure, he set a small goal of simply doubling his money. ″[My friends] would just laugh at me — 'Dude, cool. $8?' — but in my head I knew that I could double that, and double it again," he said during a Make It panel at SXSW in March.

Gamifying his side hustle made him feel like he was making progress, even if the dollar amounts were still pretty low, he said. Today, Hogue has at least 15 streams of income, including online courses, one-on-one coaching and a YouTube channel.

Hogue still works a lot — roughly 60 hours per week — because his goal with passive income isn't necessarily to create leisure time for himself, he said. Rather, he tries to constantly find new side hustles, gamify them until they're making him money, and then automate them so he can use his time to find new challenges.

Keep close track of your business's finances

You have to designate time, and systems, to keep track of your finances, according to Torres.

Torres, a former process engineer, learned a lot about finances while running a Puerto Rican food blog called Delish D'Lites throughout the 2010s. In 2019, she started another side project: a money podcast called Yo Quiero Dinero, or "I want money" in Spanish.

The foray into personal finance spawned a slew of other businesses, and in 2020, Torres decided she wanted to quit her full-time job. She started tracking her finances on spreadsheets so she could consistently gauge how close she was to making that dream a reality.

DON'T MISS: The ultimate guide to earning passive income online

After roughly a year, Torres left her engineering role. She now has seven income streams, including affiliating marketing and ads, Airbnb rental income and digital courses. Basic spreadsheets are no longer enough to track her expenses, so she invests in accounting software like QuickBooks, Wave or Xero.

The software helps her separate her personal and business finances, set a budget and "cut out unnecessary expenses in real time," she wrote. She also recommended putting aside 25% of business revenue for taxes, and finding a consultant to understand your obligations and deadlines.

Continually connect with and listen to your audience

Passive income may trim the hours you spend clocked into work — but you still have to keep up with the wants and needs of your consumers. Luckily, your audience usually will tell you what they're looking for, Jasmine McCall wrote for Make It in 2022.

Three years ago, McCall was making $124,000 per year as an Amazon resource manager. She also made YouTube videos sharing money and career advice, and one of them — about how she upped her credit score to 836, from 495 — went viral.

Commenters started requesting more credit advice, leading her to develop a digital DIY credit boost kit, available for purchase. The package includes tools like a credit dispute roadmap and step-by-step video lessons, according to McCall's website.

Next, she built a digital resume kit including interview preparation guides and templates for resumes, cover letters, references and thank you letters. Between YouTube and the digital products, it took less than a year for McCall's side hustle sales to outpace her 9-to-5 salary, she wrote.

She quit her Amazon job in May 2022. As of March, McCall and her husband bring in $143,000 per month in passive income, according to documents reviewed by Make It. Her YouTube channel has more than half a million subscribers, who tune in for personal finance tips, side hustle leads and homebuying hacks.

One of her keys to success, she wrote, is still keeping in touch with her viewers. She works just 10 hours per week these days, spending much of the rest of her time with her husband and toddler.

Want to make extra money outside of your day job? Sign up for CNBC's new online course How to Earn Passive Income Online to learn about common passive income streams, tips to get started and real-life success stories. CNBC Make It readers can use special discount code CNBC40 to get 40% off through 8/15/24.

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