You should plan about the astronomy exams preparation well before start of the exam. This includes preparation of course books list and possible use of other supporting material that you are going to use for preparation in the exam.
Try to form a group with your fellows and friends to do group studies. The group study can offer you an opportunity to practically discuss the subject matter with all members of the group and understand it deeply before seeking additional information.
Try to buy some general and interesting books on astronomy from the market, and start reading them well before the course starts. This will help you to build some knowledge base before start of the course and you can seek answers to questions in your mind while the course progresses and you attend lectures.
Follow your lecturer's notes carefully and do not miss any lecture at all. Since astronomy subject generates a lot interest and curiosity, attending the lectures regularly can help you find answers to many questions, which you might otherwise not be able to find.
Take note of each book and material recommended by your lecturers, and read them thoroughly. Since the teachers are learned and experts on the subject matter, their recommended material can be more relevant and updated one on the subject.
Start giving time to your studies more as you progress towards the midterms and final exams, even if you have been studying the subject on a regular basis since start and before start of the course. This will update you about the topics you have studied earlier.
You should also not miss the study tours to planetarium or observatories. These and other places such museums can prove to be valuable resources for learning on the subject and can add to your knowledge significantly.
With all the worries about reading, you should also give time to yourself to relax and play sports. This will keep your mind healthy and fresh and you can focus on your studies more than you possibly can while reading continuously.