Take sample tests. Before you even begin to study, take at least one pretest to pinpoint the areas that you need to study the most. You can then begin to study accordingly. Practice tests can be found in study guides at a local bookstore or even online.
Take a course. If you have time available and the resources, seek out an online or classroom course. These courses help by narrowing down the topics that you need to study. It also gives you a teacher to explain things to you should you get stuck. They also offer test taking time that is proctored and timed, just like an actual GED test.
Schedule your time. Count the days that you have until the test and make sure that you schedule time into each day to study. Ideally, you should have at least a month and 2 hours a day to study; however, this varies by each individual. Get a study guide from a local bookstore or online and separate the number of topics by the number of days that you have. Studying those topics on those days should be a top priority. If the section you are studying has a short test, take that first to see how much time you should use to study that part.
Take a post-test. When you feel that you have all the information down, take another test. If you can pass all the parts of the post-test, you should be able to do fine on the GED. If not, use it as a way to again look at what you are lacking in and focus in that area.
Relax. Do not panic on test day. If you are prepared , then you will be fine. Try to get plenty of rest and drink water to get ready. Cramming will not help you at this point, so take a break the night before and be ready.