Study regularly. If you attempt to cram for the OGT, you will likely fail. Because of the breadth of knowledge you must have for success on this test, preparing for it must be an ongoing process. Set aside time throughout the week to study for this test, working on preparing for several months before the exam.
Take advantage of in-school assistance. Particularly if you have already failed the OGT in the past, you likely have an assortment of in school help at your disposal. Visit your guidance counselor and express your concerns in regards to the test. She will likely be able to give you tips and may even be able to recommend some courses offered by the school specifically designed to prepare students for the OGT.
Determine your areas of weakness. Think critically about your skills. Look back at your old report cards and determine where you need to put the most effort. If you notice that your math grades are consistently low, for example, you should likely dedicate the most time to preparing in this area.
Ask for help. If you are struggling with some of the concepts that will be present on the OGT, ask your teachers specifically for help on these trouble areas. They will likely be willing to explain them in greater detail and may provide you with some supplemental materials to help you build your skills in the days leading up to this test.
Attempt all questions. There is no guessing penalty on the OGT, so there is no reason not to try every question. An unanswered question will be incorrect every time, so making an attempt at an answer, even if it is completely a guess, is a wise choice.
Write as much as you can on written response questions. The OGT includes not just multiple choice, but also short answer and extended response questions. These questions, worth two and four points respectively, play heavily into your score. Instead of writing just the minimum, write as much as you possibly can on each of these questions to increase your chances of earning all of your possible points.