The best thing is practice ( my maths teacher - i had a conversation w him about those really really hard circle theorems which are so hard to grasp on to and asked him how he can do it so well and he said to
practice as many times until u get the hang of it)
--- use corbett maths, or maths genie which can be easier to navigate through the types of Qs bc it tells you what grade each type is worth.
--- Also how I did well (in further maths gcse ) was I watched yt videos to explain how to do harder things before i try the Qs out myself.
--- I also used Doctor Frost maths which is for free just sign up ( and this is quite good for challenging topics ) and use your school name and it automatically marks them online and sometimes there are yt links to the question which u will usually find at the top of the practice question .
also : corbett maths is ok butt it kind of gives you easy qs at the start so if you want the harder versions of the topic, scroll to the end of the maths paper. his yt videos helped me a lot.
If you have time ( e.g like 3 months before mocks ) and want to gradually get better, which i'm trying to do, i've heard from many people with grade 9s that corbett's 5 a day helps, especially the higher plus/ higher if u wanna get those hard qs right
https://corbettmaths.com/5-a-day/gcse/lmk if anything else <3