I did the CASPER this year and got 75-100% percentile. For practise I did three of the practise tests the week beforehand — honestly I think just doing one to familiarise yourself with the structure is fine, I don't think the extra was any more helpful.
I personally found a lot of the practise questions didn't give me all of the information to make a judgement, so my typical answer to a situational question involved discussing what information I would seek next, and then what my judgement or next steps would be based on two different hypothetical answers to the information I needed. A lot of the time I decided that an issue was out of my hands and basically handballed it to an appropriate authority.
You can see yourself on the video when you speak, so if you're not used to that I'd recommend getting a bit of practise just for stage fright — even if it just means doing a bit of practise with your webcam on in an empty Zoom room.
Best of luck.