The only way to study effectively is to think about what you are reading. The best way to force yourself to think is to ask questions. After reading the material, test yourself to see if you understand it. Then test yourself with the sample tests. The tests will be timed automatically, and they will show you exactly how well you did, and what you need to study further.
Some students know the material, but still do poorly on tests.
There are some simple rules for taking tests. Check out these rules, then practice using them. Read the stem of the question carefully. Read each option carefully. Too often students pick an incorrect option because it contains one or two words that look right.