Well for me, the best thing that works is to spend A LOT of time doing exercise on previous SPM, and state trials papers rather than re-reading textbooks many times.
1. Doing previous SPM papers makes you comfortable with the format, so nothing strikes you as new during the exam.
2. Questions are often recycled from previous exams
3. It lets you know what subjects you are weak at and haven't mastered by heart.
4. Knowing how to precisely and concisely present your answer so that it saves your time and the marker,
5. ALWAYS check what's the sample answer from the answer sheet, and try your best to stick to the format.
At the end of the day you could spend endless hours reading and still not be sure or confident. Exercises makes sure you are ready and be prepared.
Hope this helps :D