Literature: I made booklets out of A3 paper with character summaries based off the plays and books I did, summarising how each character changes throughout, key quotes by/about them and then same with themes (I recommend Stacey Reay (sp.?) on youtube, she does really good analysis of characters and themes and also poetry) I recommend a structure called IFLIRT to base your paragraphs and ideas off, if you're stuck thinking of bits to focus on: Introduction, Form, Language, Imagery, Rhyme and Rhythm, Tone - always try to write about AT LEAST 2 per essay
Language: practice papers and questions, and make sure you really know what each question is looking for (use Mr Salles and Mr Bruff if you do AQA). I made summary sheets for each question on both papers, bullet pointing what I had to focus on for each of them (e.g. imagery, setting) & if you're a person that loves a good ol' structure like me(!) I recommend using PEEA point, evidence, explain (what the reader thinks), analyse (the writer's purpose) <== APPLICABLE TO LANGUAGE AND LITERATURE
Maths: literally just tonnes and tonnes of practice questions!! even just old specification papers, or I like mathsmadeeasy or mathsgenie for worksheets
The Sciences: FREESCIENCELESSONS.COM!!!! not everyone's cup of tea but I love him. I watched videos with the specification in front of me and wrote down only the very key points. Again, mathsmadeeasy has some non-examboard specific questions but they're very good for consolidating knowledge. Biology specifically is very vocab-based, so I recommend making flashcards / quizlet sets on certain questions as their mark schemes are CRAZY SPECIFIC. Also, make sure you know the required practicals, know the limitations and WHY you do everything
Geography: I made summary booklets and mind maps for each chapter of my textbook and then note cards for each case study and example. If you find geography difficult to remember (like me) I recommend mainly focusing on learning all the case studies, as the vast majority of marks are on them, and even the questions that aren't based around them, are strongly linked to them.
Religious Studies: ridiculous amount of mind maps - not focused on aesthetic, just scribbling down what you know and please make sure you have some VERSATILE QUOTES!! Didn't have the best teacher so my advice on this one isn't so great.
I didn't do French but I did German, and I seriously love Quizlet. I made so many sets and just quizzed myself daily on the bus on my phone!!
I didn't do computer science, sorry.
Goodness me that's a long rant, but I hope it's helpful and I'm down to give anymore advice or answer any questions
PS I recommend UnJaded Jade's youtube channel, check out her video on the technique 'Blurting'!