There are three things that can help inform what you revise.
All of these give you an indication of what might be in the exam and, from that, the things you should study.
Learning outcomes are in the module handbook and state what the module is trying to teach you. For example, the following is a learning outcome from a politics module.
Provide students with an understanding of the conceptual and theoretical debates surrounding political institutions and political behaviour;
It can be argued that the module leader will be looking for what they taught to come back through your exam answers so be aware of learning outcomes and what they mean. In the case of the learning outcome above, an exam would have questions that will ask students to review what understanding they have and put it down on paper to answer that question. For example, what are the theoretical debates and to which institutions do they apply?
Your exam questions will reflect the distinct areas taught in the modules and these areas will probably be seen in the lecture and seminar timetable. If you can establish what these areas are, that will be helpful for your revision.
Previous exam papers indicate the types of questions to be asked and you can use this in two ways. Firstly, it helps identify the areas covered in the exam and secondly, they allow you to practise understanding what is being asked and structuring an answer.