What is the secret to Gigi Hadid’s dominance in the fashion industry? As the naturally gorgeous model slays catwalks and editorials, the 21-year-old beauty abides by one important rule: “Being nice and bringing a positive energy to set every day,” she tells InStyle.

Hadid explains that her mother, former model Yolanda Hadid, offered the best advice for doing well at work. “My mom always said, ‘If you’re not hard-working and a pleasure to be around, there will always be someone prettier, more hard working, and more fun to be around.’”

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That humble sensibility is what keeps Hadid—who, by the way, credits “good lighting” as the key to a perfect Instagram selfie—on top of the game. Her latest gig is a starring role in Evian’s Baby Bay campaign, in which a bronzed Hadid poses as a surfer next to a too-cute look-alike baby. “My mom used to stock Evian in the house and I was constantly bringing bottles with me while horseback riding or playing volleyball,” she tells us.

“I’ve been a big fan of the advertisements throughout the years, especially the baby ads. I’m thrilled to help bring the Evian effect to life and see my image along with my baby look-alike,” she says. Hadid also revealed how she shares the same health philosophy as the brand. “We both believe that living young has nothing to do with age, and everything to do with a healthy mind and spirit.”

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Don’t think a healthy lifestyle means she shies away from treating herself. Her favorite dessert in the summer? “Ice cream!” she says.