lots and lots of luck and as it has been said, connections.
Some interning/ assiting helps a lot as well.
As for schools, are you studying fine arts or art history? I've been told that most of the art galleries prefer an art history degree. It's hard to research which school is the best, since many places have a specialization, but I know that Sotheby's and Christies both have a Business Art or Contemporary Art program that sound great for doing that type of work.