In year 11 I took Economics, 3u Maths, 3u English, Ancient History and another 2u subject. I'm not too sure about Business but I heard from a lot of my friends who did it that you just need to memorise a lot of content and you will be fine. Economics differs in that there's a lot of information...
One of the best things (in my opinion) you can do for English is to keep on writing. Practice it heaps and bother your teachers for feedback until they get sick of seeing you around LOL
Another thing is to know the command terms. By this I mean words like assess, examine, explain, describe...