how do you reflect on a book? I usually just close the book and give some thoughts to it but i feel like its not effective way to reflect by just giving thoughts. What are your suggestions? How do reflect effectively?
I believe that an answer to your question depends on many parameters, such as: What is the book about? Is it a scientific/technical book or a non-scientific book, for example, a novel? What is the age of the reader of the book at hand? How much is s/he psychologically developed? And so forth.
First of all, let me say that to reflect on a book that you have just read is not an easy process and task. In other words, you should be aware that when reflecting on a book you have read, you should not choose a shortcut to reflect on it (e.g., to reflect on what the book is about) but a demanding track and process (e.g., how novel or new is the book when compared to similar books? What is the main, say, take home message of the whole book or even of each of its chapters or parts? Do you become a more developed individual in cognitive, moral and aesthetic terms?). Parenthetically, let me say that the categories of the true, the good, and the beautiful are universal categories, regardless of how they are seen in different places and at different times. It is not a mere coincidence that philosopher Kant wrote 3 critiques, one dedicated to the true (Critique of Pure Reason), one devoted to the good (Critique of Practical Reason), and one dealing with the beautiful (Critique of Judgment).
In a nutshell, to reflect on how much the reading of a certain book made you think about these universal categories, and even contributed to your cognitive, moral, and aesthetic development is to follow a demanding track, not a shortcut, to address your question, and, with all likelihood, is an advanced way of pondering or reflecting on a book you have read shortly before or even some days ago. Of course, the more you are developed, the more you are likely to choose such pondering, questioning and, reflecting on a read book. To follow a demanding track, not a shortcut, to deal with any issue, makes me think of an answer once the Greek geometer Menaechmus gave to Alexander the Great, kind of Macedonia, an answer that is related to the mastering of geometry, and that could be applied to any subject, problem and issue. It is said that Alexander the Great (356-323 BC), king of Macedonia, once asked his tutor, the geometer Menaechmus (380- 320 BC), to teach him a shortcut to mastery of geometry. Menaechmus is alleged to have replied that for traveling through Alexander’s country there were royal roads and roads for common citizens, but in geometry there is only one road, and this difficult road is the same for all people (see, for instance, Heath, T. (1921). A history of Greek mathematics. Oxford: Clarendon Press).
I hope that I have got your question and that it shows you a reasonable way of how to reflect on a book you have read. Of course, there are certainly many other ways of reflecting on a book you, I, and other people have read.
Reflection is a process of critical thinking. Critical thinking is a process of comparing and contrasting your present concepts with other related things.
So I agree with Béatrice that you begin by identifying the main points in what you have read. Then consider each one individually and see how this main point if the same or different from other related perspectives. After you have done this for each main pint, you can consider the overall originality and value of the book.