Use any study guides provided in advance of the test to see the types of questions expected on the exam, and review any materials or textbooks that cover the appropriate subject. Most certification or professional tests have websites and study materials provided indicating subjects to expect and even practice tests, which you can take to prepare for the real exam.
Start preparing by reviewing any materials provided prior to the test with information about what to expect on it. This can indicate how long a test will take, how many questions will be on it and the types of subjects to expect on the exam. If the general knowledge test is for a particular class, then review the textbooks used with a focus on materials relevant to the exam. Secondary sources such as other assigned readings or homework should also be reviewed to provide additional information.
Tests for professional organizations or certifications, such as a teaching certification, usually have websites with additional information. Check the appropriate website for the organization or test to find out what subjects to expect and look for practice tests. Take as many practice tests as you find to gain a strong sense of what to expect on the real test and how questions are presented. Going into a test knowing the structure of questions can be critical, as it makes it easier to understand what is being asked during the actual exam.