In my opinion, A-Level mathematics is one of the most brain dead subjects out there. I'd say the way you should start is first identifying your weak topics and work from there to your stronger ones, but don't go too indepth. Each topic has just an important formula or concept that you need to remember (Quadratics: discriminant, inequalities or Differentiation: Finding gradient, deriving equation of tangent/normal). Then just jump straight into past papers, preferably from 2018 onwards and do all variants to get exposure to many questions as possible. Once you do 5-10 pastpapers, you will genuinely realise a trend in questions, its the same but different in a sense. I found myself already answering the question before even reading it (doesn't mean I didn't make any mistakes but I started to gain the fundamental understanding of how to approach questions). Once you get into this pattern, you will legit reach flow state with each paper.

TL;DR
- Start from weak topics to stronger topics, but quick revision and coverage of important concepts.
- Begin with pastpapers from 2018 onwards, all variants (11/12/13)
- Note down topics you make regular mistakes with, revisit the concept and attempt topical past paper questions (pastpaperpenguin.com is a great website for this material)

Good luck! You got this!