Excellent. Sitting for a full-length mock exam is something all students should do at least once before taking the real deal. Doing so will not only put all that you learned to the test, but it will also allow you to strengthen your mental fortitude and concentration endurance, two factors indispensable to a top-percentile performance. You can simulate the full-length test by stringing together some of the practice sets available above. Here are a few tips to help you approximate the actual conditions of the test as much as possible.
Set aside at least two hours
You need at least that much time to take a full-length test. Make sure that you're in a quiet, comfortable spot with few distractions and a strong internet connection. Sitting for the test at the same time of day as your actual exam is also helpful.
Follow the sequence of the exam
Begin with the writing section by doing one "analyze an issue" essay. The following verbal and quantitative reasoning sections will appear in any order after the writing section. The verbal and quantitative will have two sections each and 27 total questions each.
This will simulate the random order of the actual exam. If it's heads, do a verbal section; and if it's tails, do a quantitative section. Verbal and quantitative reasoning each have only two sections, so if you've flipped heads twice, make sure the last two sections you do are quantitative (i.e. V/V/Q/Q).
A coach wouldn't send you into the game cold. So why would you warm up with the exam? Make sure that the first problems you do on test day aren't the ones that count. A few practice problems and/or a five-minute free-write can help get the juices flowing.
The GRE is hard enough. So don't make the test any more difficult than it already is. That means adopting a commitment to be kind and supportive to yourself - no matter what happens. Assuming that you can find a solution to a tricky problem can often help you discover a path forward.
You've worked for weeks (or months) to bring yourself to this point, and you've seen your score improve over the intervening time. Since you know that your system works, it is not the time to improvise when the game is on the line. Stay frosty and remember your training.
At the end of the day, the GRE is just a series of puzzles - puzzles that you can successfully solve. The more that you can enjoy the process, the more confident and relaxed you'll be, allowing you to perform at your best.