Answer. Look for online tools and blogs written by students who have taken the exams already. Schaum and related names are good choices for reference books. The Universe, by Roger Freedman, Robert Geller, and William J. Kaufmann, is some of the exceptionally well-written textbooks you may want to consider when reading about astronomy. If you need an introduction to astronomy, look for Astronomy: Principles and Practice, Fourth Edition (PBK): A.E. Roy, D. Clarke. For example, OCSC prepares you with the necessary materials ahead of time. All you have to do now is go over it again and solve international astronomy olympiad problem sets. These techniques can be used with any of your preparations.