Are you talking about language/literature or both?
So I’m doing my GCSEs this year and I got 9s in both in my mocks and really the most important thing is to know the mark schemes:
For literature you need to make sure you’re hitting all the levels (what exam board are you doing?) for my exam I have to write about AO1:understanding (responses and references), AO2:Analyses (language, structure and technical devices) and AO3:context( history of the time and it’s place in the rest of the novel/play). It’s important to hit all of these ideas or you’ll be capped at a certain level. Physics and maths tutor has some great analysis for some of the texts that’s really useful and I’d recommend reading a load of model answers and stealing a bunch of ideas/ words (examiners love a fancy word like didactic, proxy, archetypal, usurpation)
For language I find it hard to explain how to do better because in a way some of it is just natural ability as my teacher once said. It’s difficult to explain how to be perceptive and have high level analysis but I would say just really think outside of the box. For language based questions pick out an individual word from a quote and think of as many things relating to that word as you can linking to it. It doestn matter how far fetched it is as long as you can back it up. Also link similar ideas and quotes together and maybe try to think of an alternate view to what you’ve already stated. But other than that it’s but practice practice practice! Read examples, get your teacher to mark yours and watch me bruff/ mr everything English/ Mr salles.
Hope that’s helpful