Do you know if it is strengths-based or competency-based? If it is competency-based, I would start out by drawing up a list of competencies and 'matching' them to my skills/experiences.
I'm not too great at VIs but one of the biggest takeaways for me was not to make it sound
too rehearsed- practice but just well enough so that you are able to answer articulately! I did this by listing what I wanted to say in bullet-point form rather than writing it all out. I then just spoke in front of a mirror, taking note of intonations and sentence structure.
Also on the day, do smile at the camera! A smile goes a long way, even if it's recorded