“ If you only want to go to a top grad school, then you’re going to grad school for the wrong reason, and the odds of you getting in are low. You should go to grad school because you want to do research, and you don’t need to go to a “top” school for that.
HOWTO: Get in to grad school for science, engineering, math and computer science - http://matt.might.net/articles/how-to-apply-and-get-in-to-graduate-school-in-science-mathematics-engineering-or-computer-science/
