I had a similar problem in year 10, and to overcome it, I read more, and wrote more essays.
As boring as it seems to write essays, they really help with your linguistic techniques and so on
Go onto the board website which your school is using, I would presume OCR, but possibly AQA, go onto their website and have a look at some past papers, and essay questions and have a go. Try to do some persuasive argument essays, they really help.