This is where a GRE prep course comes into play, which requires a decision about which one to use. For that decision, here are five characteristics you should consider:
The course you select should be comprehensive, which means it should thoroughly cover all three sections of the GRE (Verbal, Quantitative, and Writing), and have a more or less exhaustive inventory of the topics and information covered by each. A perfect score on the GRE is actually possible, but only if you cover all your bases thoroughly and review diligently.
Conciseness is also a virtue, because as much information as there is on the GRE, there is even more that isn’t, and you don’t want to distract yourself with irrelevant information. The course you select should be streamlined and follow as closely as possible the actual format and content of the GRE.
Convenience is an important factor to consider, because with the necessity of preparing for the GRE while still managing the demands of your regular studies, you will want to remove any possible barriers to your GRE prep work. Online courses are great, as long as they satisfy the other considerations, because not only do they not add to your weight load (as long as you already have a laptop or mobile device with you), they are also convenient to access when you have short intervals of downtime throughout the day.
The course you select should be easy to read, easy to understand, and easy for you to learn from. You should feel like you are making steady progress in your GRE prep, not struggling to understand the material, which should mostly be review for you anyway.
The best preparation is practice, and the course you select should provide you with plenty of opportunity in the form of a variety of practice exams. The more of these you can do the better, and the best way to use them is to take them under actual testing conditions, i.e. in a straight stretch of time with no outside references. This will not only reveal where you need to focus your studies, it will also get you accustomed to the testing circumstances, so they will no longer be stressful to you, and your performance should continually improve as you go along.