I'm not very good at the sciences myself so I can't give great advice on those, but i did get 9s in my recent mock results for english lang and lit. For english lang, just know the structure of each question really well and remember to go from the beginning to end of the source for coherency, and analyse the heck out of each quote you use, just keep asking 'so what', what does the author achieve using this simile or semantic field. For the writing, try to improve your vocab, and you can do this by learning some fancy phrases and words, and just implementing those everywhere you can. Remember to plan your writing pieces since there are many marks available for accuracy and content. In english lit you're fine so just keep doing what you're doing. To boost productivity you could set really small but effective tasks, such as, make 20 flashcards for biology, or do all the even questions on a maths paper. Preventing burnout is difficult as you are going to feel tired either way. I just keep reminding myself that its summer soon so.