Sleep is by far the most important! It is critical to be well rested on test day; you do not want to be fatigued and bleary-eyed. If possible, try to get a good night's rest for several days before test day as well.
2. Wake up at least 90 minutes before your test begins
It takes at least 90 minutes for the human brain to transition from a sleep state to wakefulness. If you wake up at 8:00 and your begins at 9:00 you will still be pseudo-asleep at test time.
3. Eat breakfast immediately upon waking
You do not want to be digesting food while taking your SAT. You have heard of food coma, haven't you? That sleepy feeling after eating a big meal? Eat a hearty breakfast full of protein and complex carbohydrates. Eggs, whole wheat bagels, peanut butter, nuts, cheese. Avoid processed sugar and fat laden foods. Ergo no Krispy Kreme doughnuts, regardless of how much they improve your morale!
4. Double check your supplies
Make sure you have several sharpened number 2 pencils, a functioning calculator, and a watch for timing yourself. And bring a snack as you will be at the test center well past lunch time. During designated breaks, you are allowed to eat and drink, so pack an energy bar, a banana, a pack of trail mix, etc. and a bottle of water.
5. Turn cell phone off
I cannot emphasize this point enough. You do not want your cell phone to go off during the exam. If you feel you are unable to completely 'unplug', then leave the phone at home to resist temptation.
6. Know your test center
If you are not taking the test at your own high school, take a test drive to the test center ahead of time. You do not want to be lost or taking a wrong turn on test day. You want to be familiar with the surroundings to minimize test day anxiety.
7. Enter the 'Zone'
Ignore your friends before the start of the test. Students feed upon each others' anxiety, so do not participate. Find a seat alone and envision success. Take some deep breathes to relax yourself. Perhaps pop in your headphones and listen to some calming music.
8. Trust your hard work and go for it!
Good luck to all! And a Krispy Kreme is a well deserved treat after the test!