Ask specific questions regarding the student's needs. For example, if a student needs tutoring for the English section of the graduation test, ask if he needs help with reading comprehension, vocabulary or analytical writing skills. This will give you an idea of what areas of the test you should focus on.
Refer to the student's study guide from class. If the student has a few math word problems on the study guide and this is the most difficult part for him, go through each word problem in detail and have the student take notes during the session. If the student has some essay questions on the guide, discuss the importance of reading a passage more than one time in order to get the main idea.
Use visual aids when necessary. If you're helping a student with the biology section of the test, you can use picture books that explain in detail the life cycles of humans and plants. This helps the student understand these concepts better than if you were using a regular biology book with not many pictures. It also creates a visual image of the concepts for the student when he takes this part of the test.
Give the student practice exams. This helps the student learn to manage his time wisely during the test, particularly if each section of the test is timed. Also use practice questions that are different from the study guide the student has. This is beneficial because on the actual test some of the questions may be trickier and he can learn how to handle them correctly.