Walmart CEO started his career unloading trailers at the warehouse—he says he got promotion after promotion by raising his hand when his boss was out of town

Doug McMillon was just 17 years old when he started working in Walmart’s warehouses in the summer of 1984.

Since then, he’s scaled the retail giant’s ranks from unloading trailers for $6.50 an hour to becoming the company’s youngest CEO since its founder Sam Walton—with a $25 million salary to show for it.

In the 30 years between starting out and taking the reins in 2014, McMillon went from promotion to promotion, holding a store assistant role in Tulsa before getting his foot in the door of HQ in January 1991 as the fishing tackle buyer and working his way up in management.

Now, he says many of Walmart’s 2.1 million workers email him asking how to emulate his success at the company. His response? Volunteer to cover your boss more.

“One of the reasons that I got the opportunities that I got was that I would raise my hand when my boss was out of town and he or she was visiting stores or something,” he recently revealed in an interview with Stratechery.

The CEO added that he would even offer to step in for his boss in meetings—whether or not he was prepared to answer all the questions that came up.

Plus, instead of brushing off queries above his pay grade and waiting for his manager’s return, he would proactively respond: “I don’t know, but I’ll find out fast and get back to you.”

“I then put myself in an environment where I became a low risk promotion because people had already seen me do the job,” McMillon concluded.

Do your job well and be a team player

McMillon gave two more tips for rising through a company's ranks from the bottom to the top like he did: Do your job well and be a team player

"Don't take your current job for granted," the 57-year-old chief exec said. "The next job doesn't come if you don't do the one you've got well."

"Be a great teammate—you learn how to lead, you learn how to influence by the way you interact with your peers," he added. "Treat them well, help them, help them do a better job."

The simple advice rings similar to that of Pret A Manger’s CEO Pano Christou. Just like McMillon, Christou is one of few leaders to work his way to the top from the shop floor.

Now, Christou is CEO of Britain’s biggest sandwich chains—and he echoed that he got to where he is today by working hard while being kind to his peers.

“I’ve watched people that have been so fixated on the next role that they really take their eye off the current job they’re doing,” Christou told Fortune. “My philosophy has always been if you do a great job, people will notice you.”

By focusing on excelling in his current job and being the best within his cohort—without “shortcutting” his peers or “stabbing them in the back”—the promotions swiftly followed.

“I was generally the youngest person or the shortest in a role within my peer group when I got promoted, most of the time throughout my career,” he said. “If you work hard and put your head down, things can happen.”

This story was originally featured on Fortune.com