If you have read a passage several times and it still doesn't make sense, try reading it aloud. Read one section at a time alternating the reading step with the reciting step, which follows. Make sure you understand each section before proceeding. If comprehension of the material is difficult, try reading paragraph by paragraph or even sentence by sentence until comprehension is achieved. If you can't do that, then go back and reread the appropriate parts until you can.
Some students find it helpful to write summaries of what they have read.
This is an excellent way to review and prepare for an exam. Verbalize your thinking. Prove to yourself that you really do know the material. It is crucial to discriminate between essential and non-essential information. The unsure student often takes too many notes.