This might not be reassuring to any of you given the late nature, but I was a waitlist w/o interview last year. I finally got a interview mid to late May and got acceptance early June. I was actually about to accept elsewhere before I got the interview invite so the timing was quite good.
As a waitlisted candidate I kept in touch with my contact which was someone else at first, but transitioned to Kim Szpiro. I sent an additional essay portraying my interest and fit, and an also sent an additional LOR. I also reached out to current students and recent alums. While I was waiting to hear back after my interview, I also reached out to the CMC to inquire about career opportunities in Tech Marketing since that was/is my interest.
Anyway that's my story and here I am in my second semester at Johnson! As someone else said, GPA and GMAT are others things to try and show improvement on if you are below class average. Otherwise, I hope this is helpful to any of you. Let me know if you have any questions!