The YouTube videos by BioRach are really good. She uses lots of diagrams for processes, which is important for OCRA. I did basically every topic question from PMT and then did all/most of the past papers in the run up to A Levels. I did the same for my mocks, but made sure to leave some papers for A Levels.
For context, I got an A in my Year 12 mocks, B in Year 13 mocks and A in my A Levels. I got 180 marks (20 marks into A, 7 marks off A*)
Ask if you have any questions