How are we revising for paper 3 ocr?

I’ve done 3 past papers and all of them I just lose marks on either silly mistakes or practical q’s, im going to brush up on practicalls but I always lose marks on some super niche topic/error in a calculation. How do I actually revise if I know the content? They’re not going to be repeating questions from paper 3 obviously so how do I revise??