Thank you for your question! My strategy is always to focus on the information that is given in lectures. Typically, the most important exam information will be given during lectures. After listening to the lectures, it is best to then look up that information in the book to have a full understanding of the literature. Of course, reading the rest of the book always adds to your understanding, but the majority of the exam questions will be based on literature that is discussed in the lectures!
You can, of course, learn all the keywords in the book by heart, but I don't think this adds a lot to your understanding of the literature. Try to take a helicopter view of the literature and focus on patterns and connections. If learning the keywords help you in achieving this, that is great! Otherwise, it is okay to not spend a lot of time focusing on it!