So far I haven't received the invitation so don't know what to expect, but took a look at the past papers. As for essays there is nothing you can learn in my opinion. You just have to be creative and prepare to discuss some political issues. However there is a part where you have to summarise a text, keeping essential information. It is worth working on. As for mathematics examination, the C section seems to be pretty easy. If your degree requires D section with this more complex maths, you will have to work on derivatives and I also found mathematical induction helpful for proving some statements. Apart from that there are standard exercises which are pretty obvious like 'solve the equation' and so on.