Amid economic uncertainty, Gen Zers, millennials and Gen Xers are increasingly taking control of their financial futures.

And their method of choice — the side hustle — is evolving.

In 2022, two in five Americans had an extra stream of income, according to a survey from The Harris Poll and workflow integration company Zapier. While the gig economy was made famous by the likes of Uber, Doordash and other delivery services, side hustlers are shifting from "blue-collar work" into "high-end, specialized" opportunities, says journalist and side hustle expert Kathy Kristof.

"Five years ago, the big stories were all about Uber and Lyft drivers or delivering for DoorDash and GrubHub," Kristof, the founder and editor of SideHusl.com, tells CNBC Make It. "Now, the big growth really is with professional platforms where people can earn six-figure incomes from home, doing everything from marketing to law."

She adds part of the shift could be because platforms like Uber and Lyft "take way too much of your earnings."

The platforms do not publicly share what drivers earn per trip. But Uber and Lyft drivers have complained that the cost of fees and other expenses that come with driving on those platforms can make it difficult to make ends meet and regulators have pushed for the companies to increase drivers' compensation.

Kristof says rideshare and delivery platforms are worth ditching for another reason: Specialized work comes with all of the benefits of a typical side hustle, but now you can earn even more cash from things you already have at your disposal, like skills and property, Kristof says.  

"Look at yourself as your greatest investment," Kristof says. "If you do that, your skills will always be in demand because you will be better [than competitors]."

In other words, you can use your existing skill sets to "become a specialist" and stand out. To start, here are the three most promising side hustles of 2023, according to Kristof:

Selling your skills and knowledge

A lot of people are making money selling what they already know, according to Kristof.

The numbers prove she's right. In 2022, over half of freelance workers, about 31 million people, provided "knowledge services," according to freelancing platform Upwork. That includes consulting in areas like computer programming, marketing, IT and business.

One option is online tutoring, with Kristof noting that platforms like Lessonface, Wyzant and Outschool will remain in demand for 2023 because "kids fell behind during the pandemic" and many of those students are still playing catch-up on their studies.

But you can educate people on skills you've gained outside of classrooms, too. In comparing the first six months to the last of 2022, Fiverr saw a 73% increase in searches for "TikTok video editing," indicating those social media skills are increasing in demand as more companies develop a presence on the platform, a company spokesperson tells CNBC Make It.

While most side hustlers are millennials and Gen Zers, according to the Harris Poll and Zapier survey, Kristof says retirees are also joining the movement. After illustrious careers, Boomers are realizing they can still capitalize on their expertise, even if they're no longer going into the office.

According to the same poll, 22% of Boomers, who range from age 58 to 76, currently have side hustles.

"Retirees are stepping in," Kristof says. "And instead of doing it for free like they used to, they're getting paid hundreds of dollars an hour just to share their contacts, accumulated information and give people good ways to solve problems."

Medical care

This category is a twofold result of the pandemic: People couldn't go into work at hospitals with active Covid-19 infections, and nurses and doctors got burned out working longer hours. A global survey by Elsevier Health found almost a third of health-care workers in the U.S. planned on leaving their current roles in the next two to three years. About one in five planned to retire, while 13% planned to leave health care entirely.

The result is a large gap in the medical caregiving industry, so Kristof predicts side hustlers or other part-time workers from all different backgrounds will have to step in.

"Now, there's a huge need for nurses, doctors and lab techs," Kristof says. "There's also a huge need for nursing specialists with and without credentials: People who are patient and kind and willing to work with people who need physical and emotional help."

Some caregiving platforms for side hustlers include ConnectRN, which hires nurses, clinicians, technicians and assistants to fill vacant shifts at medical facilities, and Trusted Health, which connects nurses with temporary positions in short-staffed hospitals and offices.

But you don't need a specialized degree to be a caretaker. There are also nonmedical opportunities available on TaskRabbit and Care, according to Kristof's website, Sidehusl.com.

Monetizing what you already own

This is Kristof's favorite type of side hustle, partially because she's tried it herself. She says that renting out high-value items or real estate can be a quick way to earn passive income.

In the past, she's used Giggster, a platform where you can rent out your house to film, TV or advertising producers by the hour. Kristof says she earned $1,455 by just getting out of the house for one day.

Renting out your home on Airbnb continues to be a tried-and-true passive income opportunity — but several platforms have dubbed themselves the equivalent for cars or boats. You can rent out any make or model on Turo and Boatsetter. Some also rent out their pools or backyards for parties and events — or even as temporary dog parks, like on Sniffspot.

But Kristof advises to stay away from renting out smaller ticket items: "You can also rent your carpet cleaner or power tools. But to me, those don't make a lot of sense because the amount that you make to rent them isn't really enough" to sustain a profit.

Side hustle trends continue to change, Kristof says, especially as free agent workers better understand their rights and the most efficient ways to make money. As specific platforms become more popular, different services can become a commodity, meaning side hustlers may have to pivot multiple times in their career, she says.

Beyond remaining flexible and open-minded, the best way to stay up to date on how to earn extra cash quickly is by paying attention to social media and watching for new, creative ways people are creating businesses and income.

"It's a matter of keeping your eye out," she says. "As we go along, we'll find that the gig economy is going to treat people better and offer them something more akin to employees or wages."

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