English - If you're planning on adapting, perfect your generic essays then look through a lot of past papers from different schools, read the essay questions and just think about how you would adapt it on the day. If you're planning on mostly writing it on the spot with a list of techniques/quotes/etc. then just practice writing paragraphs to different questions.
Economics - Probably content, but it would be worth looking through past papers, so you know which section/chapter you're less familiar with - then go through it in the book. If you don't have time to actually practise doing past papers, then at least read the questions and if you know the answer/it seems obvious, just move on. I think that MC is worth practising though - a lot of questions are quite similar in style, so you'll get the hang of it after a while.
Maths - Past papers until or if you come across a particular topic that you're constantly finding difficulty with - in that case, go back to the textbook or your class notes and read through the examples/try easier questions from the topic and then progress to harder ones.