Even though I did not take much time to prepare for the GMAT, I recommend applicants to spend at least three to six months preparing for the test. I found out at MIT, that the higher your score, the more likely you are to get in. So if you are getting 700 in your practice tests, aim for 740, and if you already have a 740, aim higher to get 760 or 770. I stopped at 700 and it could have been a problem for me. Luckily it didn’t turn out to be so. But do not take a chance on your admissions by not getting the highest score you can possibly get.
Another thing that I recommend is that you need to believe in yourself. Self-confidence is key. Most of the candidates applying for MIF are 21-22 years old and as such, they have not exhibited much in terms of work experience. The big things to getting into a MIF are your grades and your motivation. If it is something you really want to do, get an internship right after your first year of studies. Stay motivated.
Finally, work with people like Dr. Hubert Silly and MBA Center who have helped hundreds of students get into good schools. Even at MIT, I was with several students who had been students of the MBA Center and Dr. Hubert Silly. I even recommended his services to many of my friends and many of them have been admitted to Harvard, LSE, LBS, etc.