Before you begin reading, devote a few minutes to skim through the book, so that you can get a basic understanding of what the book is about. It will also give you a general impression about the different chapters of the book, what the different parts of the book talk about and what you can expect throughout it. This process will take just a few minutes and will help you understand the reading material better.
When you are reading the material, read it actively. Give the reading material your full attention, without rushing through it. At the end of every page or chapter, review what you have just read, and try to recall some key points: What did the author say in the passage you just read? What were the important points that he made in the passage? If you cannot recall what you have read at any point, go through it again. Gradually, you will find that you are able to recall information better even when you read the passages the first time.
When you are reading the material, take notes of all the important points, so that you can go through them once you have finished. Note down the most important information or arguments put forth by the writer. If you have difficulty understanding something, note it down or mark it in the book. Going through these points later will help improve your recall.
Some people find that they can recall the information better when they read aloud. You can begin reading aloud, and stop doing it once your comprehension improves. Review the important information after you finish reading the material to see how much you recall.
When you want to improve your reading comprehension, begin by reading books or articles on subjects you are interested in. Knowledge of the subject material helps you understand the reading better. As you move on to other subjects, get a general knowledge about the topic first, so you will understand the material better when you turn to harder books and articles. Improve your vocabulary, so that you can concentrate on the ideas and not on the words themselves.