1. Know your reading purpose - The way you read a book or a text depends very much on your reasons for reading it. This is why it is so important to know your reading purpose. You should read a question in your math exam differently from an entry in an encyclopaedia which you are looking at quickly to find out the date of an event. The kind of reading you do in class or for your homework is different from how you read a novel for pleasure in the summer vacation.
If you know your reading purpose - perhaps by looking first at the questions you must answer after reading - you can choose the best reading method.
If your teacher gives you something to read and doesn't tell you what you need to find out from the text or what you will do after the reading, ask her (or him)!