What do you need to know to do well in the CAT?

You are not expected to have any prior knowledge about ancient languages when taking this admissions test.  Rather, it is designed to test your aptitude - your ability to think in a way which will allow you to excel in this area.  Having a thorough knowledge of English grammar is very helpful, and in fact this is a good area in which to begin your preparation, as native speakers often find that the way in which they have learnt their native language means that they know it instinctively, rather than having a clear understanding of its grammar.  Aside from this, it is a good idea to look at the sample papers available on the university's website, which will enable you to get comfortable with the format of the exam and have some idea of what to expect.