Hi, I'm assuming you're talking about lit.
I think the reason some people seem to drop so drastically from GCSE to A-Level is that the content is quite different. At GCSE you are almost spoonfed analysis and you just have to memorise it. At A Level you are expected to come up with the majority of the analysis yourself, and the texts you study are more complex. I would also say this depends massively on your teacher, and how much help they are willing to give. I think the best thing you can do is finish your GCSE course so that you have a base knowledge and then get your hands on the texts you will be studying next year to get a headstart. Really try to understand themes, characters etc. Also, a big part of English A Level is crafting sophisticated essays that get your point across whilst also just generally sounding good, so revise your English language stuff as well so that you can excel on this part.
Good luck!