Jean Fan (a recently-graduated hotshot PhD Bioinformatician) gave some really fantastic tips here: https://jef.works/blog/2018/02/26/phd-program-interview-and-application-tips-and-advice/
I asked a similar question to two senior postdocs in my lab yesterday, and they were more succinct. They said (1) have a 1-minute summary of your current and past research projects. It's hard to do, and doesn't actually reflect your potential to do well in grad school, but it makes you look well put-together, (2) have a quick summary of why you like that program, and (3) remember to relax and let your interviewer talk about themselves!
Good luck! You're going to do great!
pennypeng reacted to VirtualCell in What should I prep for my interviews?