There are various ways of preparing for an exam, each of which suits individuals with different learning habits. In general, the best way to prepare for an exam includes a knowledge of what to expect (something that is explained in the syllabus), the type of exam paper (multiple choice type or essay type, etc.), the duration, purpose (class test vs. Job entrance exam, etc.), etc. If it is a school test, the course instructor may already have mentioned the topics that you can expect. If it is for a job, the syllabus would give you some idea of topics that you need to prepare and you can find some standard reference books for that. The test format would also be known to you. For example, multiple choice questions require speed for attempting all the questions. On the other hand, essay or descriptive type tests require you to write a lot on specific topics. Your preparation would therefore be different. For a descriptive type test, you need to study about various topics in detail, where for multiple choice test, you need to cover the breadth of the course. Another useful way to prepare for the test is to simulate similar conditions at home and try attempting a sample test. This helps in mentally preparing someone for the test.
Hope this helps.