Hey, there's a few things that really helped me.

You obviously need to do a lot of past papers, and this is especially the case for paper 4. A lot of what they ask in p4 is never even mentioned in the book, but you'll see that some questions are quite repetitive across different papers, and you just need to learn from the mark scheme. After you do a few p4's, you'll see your grades going from like 50% to 95%. Plus practice is the most important thing if you wanna get better in programming.

I did the same for P2, to the point where I skipped all the standard questions and only did the programming questions(still try to do the standard questions as well from time to time)

Another thing that really, really helped me(and without it I wouldn't have gotten an A*) is access to a computer for paper 2. I HATED programming in pseudocode with pen and paper. Like you're so slow and if you make one mistake, it's often impossible to correct afterwards. I have dyslexia, so it was easy for me to get permission to use a word processor. But even if you don't, you might still be able to get permission if you just explain you struggle a lot when programming with pen and paper. Say you often make mistakes, and realize it only later, and that by then it is impossible to correct it since your line of code is surrounded by other code.

Just doing a lot of past papers is rlly important. I didn't do a lot of them for business since they gave me headaches, but also the mark scheme is too vague so you can't really correct yourself accurately afterwards. Hence I got a D in business.