If what to wear is the second most important question, what’s the first?
I would say that the most important is to always find out who will be on the interview panel. Get their names and job titles. Look them up on LinkedIn but do not try to connect before a position is offered. See if you can find them on social media. Do not “friend” them. Read what they say about themselves, their company and what opinions they express and causes they support or oppose. Look at their photos. Why? Because, as you walk across the room, you can work out which of the panel is whom and, because you know their functions, you know which one is most likely to be the decision maker.
It is important to try to know who holds the authority. Often it will not be the one in the middle of a panel of three who drives the interview. Often it will be the one who sits quietly, not making many notes (that’s what the others are doing) and who does not ask many questions. When that person does speak, you will note that the others become almost subservient.
That is the person you most need to impress. You should make certain that at least some of your answers are directed to him.
It is important that no member of the panel feels left out. Get a group of friends and practice, three on one side of a table, one opposite. The one sitting alone should learn to look at the eyes of each of the panellists in turn while answering. Somewhere between half and one second is good: any less and you look shifty, any more and you look a bit strange.