Maths and Physics are very similar to revise/check if you can do it. Just do plenty of questions for each unit/chapter and if you can't do it, then look the answers up in your books or notes. If you still struggle to find the answer then look at the mark scheme. When you are confident you have a large understanding do all of the past papers and learn the mark scheme.. this really really REALLY helps
As for biology i'd say flash cards are a good way of remembering everything and again do past papers
Sorry I have no idea what the economics courses are like