How can I plan and improve grades?

First thing you wanna remember is to not panic; in the majority of cases, people are predicted lower in y12 than their y13 results. To improve the B in further maths to an A, i would just really recommend going into the textbook, finding the parts you struggled with, and doing the questions from there without help (and if you need help, first look at the start of that section and try, then examples and try and only if you're stuck for 15+ minutes ask for help or look up solutions, i know it sounds long but this will get it into your head better than anything else will). Same with regular maths tbh. (If you're struggling a tiny bit all around however, just focus on occassionally revisiting and sharpening old topics however you'd like to). Computer Science, other than programming should be mostly terminology or otherwise simple things (other than maybe depending on your strengths boolean algebra and normalisation) at this point so use flashcards to learn and you're good (i recommend anki). For physics, if you can get access to the textbook and do something similar to maths, perfect, if not, find your old topic tests, see where you went wrong, learn the correct things, etc.

Thanks a lot, made a note of it. I guess textbooks help the most than anything else. Appreciate your pointers. Good luck !