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 give you the opportunity to strengthen your mental fortitude and concentrational endurance: two factors that are 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 four hours
The GRE is long - and you need at least that much time to take a full-length test (including breaks). 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 useful.
Follow the sequence of the exam
Begin with the writing section: an Issue prompt followed by an Argument prompt. Then follow with five, alternating 20-question problem sets. Just like the actual exam, one of these sets will be the unscored experimental section. Practicing with an additional set will give you a sense for how long the GRE really is.
This will determine which experimental section to give yourself. If it's heads, give yourself an extra verbal section (i.e., V/Q/V/Q/V); and if it's tails, give yourself an extra quantitative section (i.e., Q/V/Q/V/Q).
Making effective use of the time between sections is essential for high performance. Give yourself one ten-minute break after the second 20-question problem set, and five one-minute breaks between all the other sections of the test. Use your longer break to have a snack (chocolate?) and go to the bathroom.
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 with 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.