People have already given good advice for long-term strategies, so I'll give some tips for the day of the test itself.
First of all, the Princeton Review book suggests that you do practice GRE problems the morning of the test as a warm-up. I didn't do GRE problems the morning-of, but I did do some logic puzzles to pass the time on the 1.5 hour bus ride to the test center (free Kindle games are great!). I think doing that definitely helped me to focus and get into the right mindset. I really, really like solving puzzles, so by playing puzzle games, I was able to convince myself that the GRE was just more puzzle-solving. By the time I started the test, I was actually really excited about the "game" I was about to play (and of course I wanted to win).
Second, the GRE has built-in breaks, but if you need longer, you can use the instructions screen for each section as a sort of bonus time to mentally prepare. Basically, before each section, they will give you a screen of instructions on how to do that section. If you found the previous break was too short, just stay on that page and don't start the section yet. I suppose it's possible it will eventually time out and auto-advance (I didn't test it), but I know at the very least it will give you an extra few minutes. Also, maybe I'm weird, but I found it comforting to read the instructions multiple times, even if I'd encountered that type of section before, because it gave me a "nothing I'm about to see will be unexpected, I can do this" sort of confidence. Hah, okay, I'm pretty sure I'm just weird.
Finally, don't get discouraged by tough sections! I know it's easier said than done, but keep in mind that it's entirely possible that the tough section is experimental and isn't going to affect your score at all. My very first section was a super brutal quant section, and I was sure I was doing horribly. The next quant section I hit was way easier, and because the test is adaptive by section, I was convinced that I had been put into a lower score band. Then I hit a third quant section, which was also fairly easy, and it occured to me that the hard one might've been experimental. Don't let a possible experimental section stress you out and cause you to lose confidence!
For the record, my scores were 165V, 170Q, 4.0AW. Hope these help at least a little, and good luck!!!
