Usually, video interviews consist of around 3-5 questions and you have 1.5 minutes to answer each.
Questions are very generic, like why law, why our firm, what recent commercial story you’ve been following and how it will impact our business, demonstrate example of leadership, demonstrate where you overcame a challenge - to name a few
The best way to prepare (at least for me):
Find online as many questions as possible and come up with sample answers. However, don’t write the answers down word for word - only keep bullet points with key things that you have to say. Otherwise, you might stumble in the video interview if you accidentally miss out something.
Find online (any graduate brochure) all the competencies that firms look for in candidates and find examples where you demonstrated them. Again, make bullet points.
Prepare at least 2 commercial stories (personal advice - don’t speak about Brexit, way too generic).
Record yourself on your IPhone and then watch how you answered the question within the time limit. The most cringy experience I have ever had in my life, but it really helped me with acing several video interviews.