You really need to do some more basic research.
First, take a look at the rankings publications - US News, Businessweek, FT. Read the articles that come with these rankings. Lots of useful information as well as info on how the admissions process works.
As for your GMAT, do the best you can. Again, you can get stats on the incoming GMAT averages and ranges in many of these rankings publications, as well as on the schools' websites.
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