How to get into Northfield Mount Hermon?

Hi, I’m an 8th grader wanting to attend NMH as a 10th grader boarder. My grades as of Spring term right now for 8th grade went A, A-, B+, B, B and I played Fall term Volleyball and Spring term Tennis. I heard that NMH doesn’t care about grades because they care more about if you’lll contribute to society? Can anyone tell me how to ace my future interview? Should I make a portfolio for art? I plan to try really hard during my 9th-grade year and hopefully get all A/A-'s too. Is this enough??