Mark it on your calendar. When you know the test date, put it down on your calendar and figure out the number of days you have to study.
Test yourself. As soon as possible, take a practice test to find out what you know and what you need to study. Find a practice test that's similar to the one you'll be taking.
Work on your weak areas. Review the subjects that you were weakest on. If certain types of questions give you problems, focus on understanding them better. Create a ranking of your problem areas so you can work through them.
Make a daily study commitment. Block off some time each day to study, ideally at the same time each day.
Understand the test format. Becoming comfortable with the style of questions will help you to do better, even if the questions are different from the ones you study.
Take more periodic practice tests to check your progress. Change your study schedule if needed.
Pace yourself through each section of the test. If one section is giving you difficulty, skip it and come back to it later. You want to have enough time to finish the parts you know well, so don't spend too much time struggling in one area.