Hey, don't know if these tips will work but when i studied for my exams i had used HegartyMaths, went through a lot of past papers, read a page of say a CGP Biology book and wrote what i could remember, and the stuff i couldn't remember use flash cards, and Science and Maths by Primrose Kitten, she goes through everything. Hope this helps!
If you work hard you can definitely get good grades but I would recommend starting SERIOUS revision as early as possible, specially if you have a lot of subjects otherwise it can get pretty stressful towards the end. As for revisions tips, I'd say go over previous notes/textbooks/revision guides, practice exam questions from past papers and watch a ton of youtube videos to clarify things you might be struggling with (Freesciencelessons, Science with Hazel, myGCSEscience, HEGARTYMATHS, mrbruff, and Stacey Reay are really good channels). Good luck