Don't be generic
You cannot write one general "fit all" essay and send it to several different schools. Each business school has painstakingly carved a niche for itself, and each school focuses on certain facets of business education, approaches to study, delivery, methods of evaluation, internships and placements etc. No two schools are the same, and you should not treat them as such. If you fail to address these in your application and more so if your application does not relate to any of these, it will most likely be rejected without a call for an interview. Business schools check that you have done your homework before you submitted your application. They appreciate honest, authentic search for common goals and understanding, not a common essay with no relevance to the specialties the schools have acquired over the years.
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You are focusing too much on the past instead of the future
Your application should not be devoted exclusively to past achievements. You need to show the admissions committee your vision for yourself in the future, what you want to accomplish as a leader, and what you hope to bring to the table. You should also include the skills that you hope to learn in business school and explain how they will help you achieve your future goals. After all, it is important to the school to help you grow as a person and a professional. You want business school to teach you what you currently lack.
You should not get recommendations from people who do not know you as a person or as a student
If you approach someone just because he/she is well qualified and holds a high position, or title, but does not know you at all, it will reflect in his/her recommendation letter. The admissions’ committee will see a huge difference between a recommendation letter written by someone who knows you personally and one from someone who does not. Always remember the admissions’ committee and its members sift through thousands of applications, and they select those that stand out as unique, personal, and memorable. Only someone who knows you well can correctly appraise your personality, your ability to learn from mistakes, and is truly invested in your future.
Choosing your target schools based on rank and reputation
Before you decide on a particular business school, you should research the school's faculty and its course offerings, its placement record in the past and which companies visit this school for internships and final placements. The main reason for this is that each school has its own specialization and if you want to work in a specific industry post-graduation, you should pick a school who can best position you for the job of your dreams. Secondly, when the admissions committee asks you in the interview why you chose their school you need to have an authentic and convincing response. Business schools accept students who are passionate about being a part of their school, not candidates who only care about its rank and reputation.
Leaving everything to the last minute
You need to prepare ahead, having well thought out plans, essays, research on the school's reputation and rank. Your essays should not sound negative or whining, and you should not cram too much into one essay as volume can never substitute quality. You should avoid hackneyed ideas and clichés. Admissions committees have read many applications and want to see something fresh and out of the box. The admissions officer/committee should see the passion in your documents. They should not see grammar and spelling mistakes. You should proofread your documents again and again. You should go over at least two-three iterations before you submit your application. It could be a good idea to show your application to someone senior, maybe a university professor or a friend who is well placed in the industry, and incorporate their comments in your application. All these require time and you cannot do these in a very short time without any planning.
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