GCSE Pearson Edexxcel MANDARIN

I got a 9 in both French and Chinese. I speak Chinese at home so it was really easy for me (except needing to learn how to write some stuff) but I went to Chinese school where they taught some exam prep stuff so I'll try give some advice I used for both and I'll try make it applicable to you.
Reading/Listening: For Chinese I didn't need to study and I wasn't given any exam prep (that I can remember) so I'll give some tips I used for French. My French teacher suggested to watch Peppa Pig in French with subtitles on or just put French subtitles on anything on YouTube. Kid-friendly stuff probably works better because they're trying to make you learn language.
Past papers are also great for getting some experience, especially getting used to the style of questions they ask and stuff they could catch you off guard with. If you're confident enough in your reading you could ask your parents to read the texts in reading papers out loud and you can try answering the questions, turning it into listening practise.
Writing: In terms of memorising characters I wrote them out a bunch and then I'd test myself on them. You can either write down the pinyin on a piece of paper and then use that as your 'test' and try writing them from memory and repeat this over time or better yet give a list of words/phrases to your parents and get them to read them and you try write them (like a spelling test).
To practise the essays you can use past papers or just make some on your own. Choose a topic and write some bullet points and try write about them. I don't know what classes as a good piece of writing (other than no grammatical errors) but my thoughts would be using some varying sentence structures (e.g. 不但/不仅... 还/而却... ; 虽然... 但是...) and not repeating yourself a lot.
For translation it was just learning how to write more vocab for me and again I did the testing thing mentioned earlier to try and remember how to write as much stuff as I could.
Speaking: Edexcel has time requirements for speaking which I had to get used to because AQA (my French exam board) doesn't do that. The easiest way to practise would be to use past papers to practise role plays and photo cards (don't worry about running out, there's a ton of them). Give yourself the 12min to prepare answers and see if you can speak for the required amount of time (2-2.5min on role play, 3-3.5min photo card). One method I was taught for describing the photo was PALM - People, Actions, Location, Mood.
For the conversation you can write down a bunch of questions that could be asked for each theme and after a while choose one of the themes and go through your questions list and see how much you can say for each or ask your parents to do a mock conversation (or just the whole thing) with you. For French we were given a list of 60 odd questions and we had to write out a response for them. Then we turned them into flashcards with the question on one side and one word/phrase bullet points for an answer in English on the other side so we could use that side as prompts.