Fun fact, my very first technical interview was with Microsoft for the Explore program which I was taking Data Structures. I was asked about Fibonacci, to implement it, and then we talked about its time complexity. He followed up asking how my implementation could be improved. I recommend saying everything going through your head out loud. They want to see how you think. Also, make sure to explain your thought process before writing anything on the whiteboard. I even like to confirm with the interview if they like my initial idea. Then I pick up the pen and go ahead, explaining every single thing I write. I mention corner cases as they come to my head. And at the end, make sure to test your code and walk through with examples!! Even if it is the easiest problem ever, it is so important to show that you’re thinking through everything.