One type of good boss really sticks out from the rest, says real estate entrepreneur Barbara Corcoran: someone who prioritizes their employees' success just as much as their own.

Great bosses understand the "cardinal rule" that "I work for you, you don't work for me," Corcoran said in a TikTok video posted in March. She's practiced that philosophy ever since she launched real estate firm The Corcoran Group in 1973, she said.

"That's [been] my attitude my entire life. What can I do for you? How can I make your job easier? What do you like to do? What would you rather do? " said Corcoran, 76, who ran her firm for almost 30 years before selling it for $66 million in 2001.

Her outlook might sound counterintuitive: Employees do, in fact, work for their bosses. Rather, Corcoran's suggestion is more in line with the idea of "servant leadership," where leaders try to set their team up for success just as much as themselves.

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Servant leaders typically believe that an environment where all employees can thrive ultimately benefits the entire organization. "You'd say, 'Well, that doesn't put the boss ahead,'" said Corcoran. "It does. Because as they get stronger and go up the rank, they carry me for a free ride ... That's how it goes."

Bosses with a servant leadership mindset are a major "green flag," according to Deepali Vyas, the global head of fintech, payments and crypto practice at Korn Ferry.

"Managers that master the balance of emotional intelligence and not being so rigid — that's a good boss," Vyas told CNBC Make It in October. You can tell if a leader possesses these soft skills by asking a simple question, she added: "How would your current team describe you and your leadership style?"

A good boss' answer probably includes hallmarks of traits like selflessness, empathy or flexibility. Maybe they set time aside each week to teach an employee a new skill, despite their jam-packed calendar. Or they covered the cost of an employee's new certification, and helped them move their schedule around to study.

Just be wary of a boss who struggles to effectively establish authority or meet business goals: "I've seen well-meaning servant leaders fail to spend as much time and energy on planning and executing to achieve company goals as helping individuals achieve theirs," leadership expert and ex-Procter & Gamble executive Scott Mautz wrote in a 2021 blog post.

The best leader is usually one who "empowers you to grow" professionally, Vyas said. That kind of attitude inspires employees to go above and beyond at work, and always put forth their full effort, Corcoran noted.

"The key to being a big boss, a growing boss and a great boss is really understanding you work for who's working for you," she said. "It's as simple as that."

Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank," which features Barbara Corcoran as a panelist.

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