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1) Know how to build good relationships and a good reputation with people who are in the market or adjacent to it. That's the easiest and fastest way to get in. Hopefully you've been lucky enough to land an internship or two before you graduated, and kept in touch with the managers.
2) Your GPA better be something above 3.2, it helps a lot especially if you're not Ivy League, and you have to know your stuff. If you say in your resume that you know C++, you better be able to explain that language's nooks and crannies well enough to make an intelligent assessment of how a sequence of C++ code will behave, even if you've never seen it before.
3) You have to be able to show persistence, pragmatism and creativity in the way you solve a problem. That's the science part I guess.
4) You should be an intellectual, and know more than just computers and math. That helps a lot with creativity in problem solving.
5) Ability to find the needle in a haystack.
If you are currently enrolled as a CS major student, you should be learning different computer languages such as c+, c#, .net, java etc. These languages are going to be your key skills to find an intern or a job.
If you are not in college yet, go make an appointment to talk to college advisers at CS major, they will provide you the current needs of the market.