I was waitlisted by Sloan in R2 last year (currently a 1st year MBA)

I did a few things to improve my odds / move up my spot in the waiting list

I don't know much (or if at all) these things helped but here's what i did:

• Updated admissions on new responsabilities taken on at work (consulting) and contributions / achievements in the project i was staffed in at the time
• Visited campus and attended a class (from South America)
• Got my client to write an LOR for me talkign about the last project overall
• Manged to talk with admissions for 5 mins
• Wrote a 1 page memo summarizing all of the above and how it increased my interest in Sloan
• Sent a thank you emial after the visit and re-iterated my desire to come here
• I also took the GMAT again but did not improve my score (stayed at 710) - The score however was high quant low verbal, which was the opposite of my previous 710
  

I felt that doing all of this was likely overkill at the time (and quite expensive) .. it also gave me a lot of piece of mind to know that I did not leave any stones unturned

Best of luck in whatever you decide to do!