You will have to do very well on the GMAT to be considered at Harvard - likely 730+ (if not higher).
For this you need genuine mastery of most topics. There is no easy way to achieve this, but it is doable. The early plan for you will be to focus intently on all of the material and especially answer choices. Read and review correct and incorrect choices so you understand why things are right and wrong. Ultimately, there are patterns and you have to discover them.
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Jim Kernan is the Director of GMAT Operations at Stratus Prep and author of GMAT Materials for GMAT Prepster.