You absolutely must exercise. This is something I learned from a colleague back when I taught test prep (I taught GMAT prep): determine what time your exam will be and exercise at that exact time the day before the exam (or on more days if you have that flexibility). Among many other good things exercise helps against anxiety.

Another absolutely crucial - cannot stress its importance enough! - compoment of success is being well hydrated. Mental acuity is diminished by even the slightest degree of dehydration, and you need all your mental faculties present at your service. That means taking a water bottle with you to the interview and sipping from it.

A light snack with protein is very helpful. A peanut butter sandwich, some nuts and cheese etc. - if you are applying for a position in dietetics, you know the drill yourself.

Make a list of your good qualities and relevant experiences, too.