Study the leaked iOS source code and surprise them ;) Other than that and on a more serious note, Leetcode and algo and data structures are your friends. Maybe

Study the leaked iOS source code and surprise them ;) Other than that and on a more serious note, Leetcode and algo and data structures are your friends. Maybe read a thing or two about UX, like the book "Don't make me think" that got mentioned here a couple times. Good luck!