Before you go in, prep like you would for an interview. Know your strengths and weaknesses, and any relevant experience you have. Think about how to communicate that. Consider questions or topics that they're likely to ask about that will open the door for you to talk about stuff.

All in all, your test scores and academic history will tell them a lot about your capabilities. You'll probably be talking a little about specific work experiences, and then about how you approach work situations in general. Epic is a pretty unorthodox environment, but like anywhere else, they're looking for bright, motivated people. So be that.