This is Kevin O'Leary's No. 1 job interview tip

This is an excerpt from the CNBC Make It newsletter. Subscribe here.

Millions of Americans have been quitting their jobs this year in a movement dubbed the "Great Resignation."

In March alone, a record 4.5 million people resigned and there were 11.5 million openings, according to the Labor Department's latest Job Openings and Labor Turnover report.

As millions of people search for greener pastures, I spoke to "Shark Tank" judge and O'Shares ETFs chairman Kevin O'Leary to get his advice for job applicants. His No. 1 tip? Tell the truth.

"Great HR managers have an innate skill to sense bull----," O'Leary said. "They know when you're lying to them because [detecting that is] what they do 24/7."

Rather than exaggerate your abilities or interest, O'Leary says it is better to be transparent and honest about the parts of the role that interest you the most.

Showcasing your strengths and interests can make you a more appealing candidate to a recruiter, even if they're outside the job description.

Instead of telling the interviewer what you think they want to hear, "ask for things that you want to do and tell that HR manager why it would be good if you got those attributes in your job," O'Leary says. "The reason they're hiring you is that they want you to advance the mission [of the company]."

O'Leary also emphasizes that it is important to familiarize yourself with the company's mission, "no matter how big or small it is," before you sit down for your interview.

"When you understand the mission and you can start explaining how you can add and enhance that and get to that goal faster, you're going to find a lot of accommodation to pull you into the organization," he says. 

And remember: Now is a great time to be looking for a job, as O'Leary previously told Make It. Prospective employees "have lots of flexibility" to ask for what they want, such as higher pay or the ability to work remotely.

"If you don't want to move into a big office, you don't have to," O'Leary said in February. "There's so many companies that today will let you work from home or work from a distance. It doesn't mean you never go in, but it means you have flexibility."

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