I've been to a couple recruiting trips and I'd say a) software engineer internship b) hackathon experience c) side projects d) contribution to open-source platforms are a couple things that could stand out from a resume. In terms of the interview itself, having a good knowledge about basic data structures and algorithms could help a lot. Practicing coding questions on your own prior to the interview is also something to consider.
Know all your COS 226 algorithms and work through practice interview questions from a book like "Cracking the Coding interview" or "Elements of Programming Interviews." If you haven't done software interviews before, find someone who has and practice in person. When I was a student, the ACM club held mock interviews that I highly recommend if they still do them. I don't think I was asked anything too crazy in my interviews but it probably depends on your interviewer. Also, don't get too stressed about the onsite. There's only one 45 min interview and then they show you around the campus and stuff.