I always like to look up "common interview questions", or practice on HackerRank and read cracking the coding interview. In school we get a vast amount of knowledge but it is easy to get rusty if you haven't looked at something in a while.
Another tip I have is to view an interview as not only an opportunity for the interviewer to evaluate you, but also for you to evaluate the company. "Fit" is really important and you also want to make sure that this is a working environment that you would enjoy.
I had one 30-45 min technical phone screen. Once I passed that, I was sent a form in which I could choose whether I wanted my on-site (final round) interviews to be for the program manager (Microsoft's title for product manager) or software engineering intern position. I chose program manager intern, and had four 45-min interviews at Microsoft's HQ, with a break halfway through for lunch. They covered design, coding, management skills (essentially people skills--how did/would you resolve ___ conflict in ___ team?). Lots of questions like "how would you write an API for..." and "how would you design a product for..." Don't get caught up in details and don't stall. Throw out many big-picture ideas and the interviewers will tell you what they want you to elaborate on. Reading PM interview guides can't hurt but only use frameworks when they really make sense for the problem.
Be sure to research the company culture and how the brand has evolved over the last 5 years. Being able to speak to the greater Microsoft's current product initiatives and seeing the big picture for how every retail store supports that effort is critical. Energy and a growth mindset are non-negotiables.
It's helpful to glance over the usual interview prep, but also be ready for a design question ("Tell me how I would approach building ______ for _____"). Overall just be friendly, have a good conversation, and ask the interviewer questions too.
Know everything about any company, not just Microsoft, it is advised one goes through their websites, blogs, social media accounts and recent news articles about the companies. For example, case in point, Microsoft acquiring GitHub