Preparing for a master's degree is definitely not the same as studying for a final exam or cumulative test. Master's or graduate programs generally last two to three years, and most programs require students to have completed a bachelor's degree first. One of the best ways to prepare for a master's degree is by choosing a bachelor's major that focuses on the fundamental field of study you wish to pursue in your master's. Additionally, in order to be accepted to most graduate programs in the United States you will be required to take the Graduate Record Examination (GRE), for which there are plenty of resources to help you prepare.
Determine the area of specialization you wish to pursue through your master's degree. If you have not decided, explore the programs out there within the general area of your interest. For example, within the field of biology you will find specializations in biology education, micro-biology, marine biology, molecular biology and organismic biology, among others.
Do research on all the colleges and schools that offer the graduate program you want. Explore the curriculum and take note of the required course work covered throughout the program. This might help you choose the adequate major, if you haven't completed a bachelor's, or it will help you see what areas to work on before enrolling. For example, a student pursuing a master's degree in marine biology will need to be proficient in many life sciences courses.
Take as many courses as possible in the areas of study that will be part of your master's curriculum. This will give you a good foundation.
Contact an adviser from the school where you wish to pursue the master's program. Find out if the school offers preparation courses, summer internships or other career development programs geared towards your field of study. Most colleges provide programs that help future students.
Prepare for the GRE. Understand the format of the test, the areas covered and enroll in a preparation course, if possible.
Take GRE practice tests to determine the areas where you need to improve. Take writing courses, if you feel you need to improve on the essay sections of the test. Monitoring your scores will help you see what areas you need to work on.