Great question...
Personally, I've always struggled to prepare for interviews as I have no idea what style the interview will be, even when interviewing for a promotion, the styles have been very different than I expected.
The one I thought I had no shot at was the easier and to my surprise we basically a one on one and we talked about Excel the entire time as they needed an excell person and that's my specialty in this new group.
The direct promotion right above where I was, which I thought would be the easiest, was 3 person group, and there basically was no back and forth, instead they just asked questions, I tried to answer and got silence in return. And they were asking about extreme niche part of the job, in which I think no one at my level would have experience in that yet, as that was almost two promotions above level type thing.
