Does anyone have any HUGE A-level comeback stories?

would you mind giving any tips

chemistry is more content than it seems, without understanding the theory behind it you won’t be able to apply the knowledge. i’d recommend watching YouTube videos (allery chemistry, machemguy etc) to consolidate knowledge after lessons, then do exam questions - if you or your teacher have access to chemsheets, do their questions first !!
also, making sure you are aware of common questions that come up every year as exam boards will just repeat questions, so make sure you’re doing papers and exam questions.
overall, chemistry is a subject that is easy to fall behind on and its difficult to make up so having a good foundation of the previous topic before you move onto your next is crucial. i hope this helps 💓

Mathematics. Economics. Geography.

for content i use flashcards on Anki, but for inorganic topics i would recommend memorising and blurting the notes on chemrevise, if you remember those notes you’ll be getting really high marks on organic questions easily!
for calculations i start with basic questions using chemsheets then i do exam qs. my favourite youtubers for learning how to do these calculations is allery chemistry and machemguy - allery chemistry also has really great videos for explaining content.
resources i use: they have loads of topic specific exam qs !!
i just do the questions on pmt but if i find that i need more practice i use the other resources - i would recommend doing loads and loads of exam qs for amount of substance, acids and bases, thermodynamics and equilibrium as they are topics that ALWAYS come up and often account for a lot of marks - esp if you’re doing AQA
hope this helps !!