Take a practice geometry exam in preparation for the GED. Practice books are available at libraries and bookstores; exams are also available free of charge on the Internet. Grade yourself on the practice geometry exam to determine how much help you need in the subject.
Study to fill the holes in your understanding of geometry. This might include studying geometry vocabulary words and terms; reviewing the types and degrees of certain angles; studying the names of various triangles; reviewing how to measure vertexes; reviewing how to measure area; studying how to measure and use pi, circumference, diameter and perimeter; solving word problems and understanding the Pythagorean Theory.
Take another practice test to see how your study is progressing. If your scores aren't satisfactory, continue to study and take subsequent practice exams so you'll continue to improve.
Get plenty of rest the night before the exam. The morning of the test, eat a healthy breakfast to help you stay alert, energized and focused. Do not drink a lot of caffeinated beverages -- you don't want to be filled with nervous energy.
Take your time when doing the geometry portion of the test. The questions are multiple choice; read each question carefully and consider each option. Use a scratch sheet of paper to work out the problem; if your answer doesn't match any of the choices, don't panic. Do the problem again if you have the time; if you don't, make an educated guess.
Relax. Geometry is only one part of the mathematics portion of your GED exam. You can still do very well on the test even if you don't answer every geometry question correctly.