A* essays at a-level are hard but possible. the main tip is that for context (the time surrounding the writing of the book) you use exact figures and dates. it doesn't say it explicitly in the mark scheme but if you dig deep in the mark scheme or read A* essays you'll find its a common theme. So exact dates of, for example if you did American books, the date of the Great Depression, the number of migrants who moved from Oklahoma, the average pay etc and work it all into your essay.
I realised this about 3 weeks before my a-level exam and I went from getting around 21- 23/30 in class to, in my final exam paper in American, 29/30, in literally 3 weeks literally because I changed this 1 thing. my exam board was OCR for reference however im sure its the same for other exam boards.