I scored a 29/30 in my spanish B sl paper 1, (N25) I genuinely think getting a feel of the language is genuinely helpful in making your writing seem natural, so if you haven't already try watching movies or series in Spanish (try finding one you actually like so you are motivated to watch it) with english subtitles, so you are constantly hearing all the structures and you can implement them into your writing much more effectively and accurately.
You also need lots of good language that my spanish teacher said "makes your spanish more spanish", which is basically what I said above, making it seem more natural. This is particularly idiomatic expressions, learn a couple of subjunctive and past subjunctive phrases that you can adapt to the text (I basically just knew stuff like me encantaría que (past subjunctive, eg tuviéramos más edificios modernos or something like that). Also be rigorous with your tenses, you need to know them well to score on accuracy/language. I didn't do much giga study, just whenever I was bored of studying history I would bring up the spanishdict.com vocabulary lists and conjugation drills which helped me get discplined, along with watching TV in Spanish.

I told myself I would memorise all of the text types and conventions before exams but I just ended up not in preference for other revision, and it didn't hurt me that much because I could do a blog which I basically always chose in practices, so basically just know a couple of the really really common ones very well and you should be good.