Here are some tips for waitlisted candidates:
1. Take the GMAT again if you think there’s some chance you can improve your grade significantly.
2. Visit the campus and request, in advance, a (second) interview with an admissions officer.
3. Get a couple more support emails from students/professors/alumni. Email them to the admissions office.
4. Write a cover letter to the head of admissions detailing recent, significant, positive developments in your career / life (GMAT improvement, new job, promotion, distinctions) and restating your strong interest in the program.
5. If the school doesn’t object to additional recommendation letters, get an additional recommendation letter. If there was a significant development in your career (new employer, promotion, distinction) – you can get an additional recommendation letter covering this new development.
6. If the school allows additional essays, select a topic that adds information beyond your original application and write a new essay.
Good luck!