Don't make yourself crazy - While the LSAT is very important, don't lose perspective. Everyone in the test center is basically in the same situation you are in. If you panic and start thinking about how everything comes down to the LSAT, you will lose the focus that is absolutely essential in taking the test.
Get a good nights sleep - The LSAT requires high levels of concentration. Therefore, make sure you get enough sleep the night before the test to make sure your mind and eyes are well rested.
Be careful what you eat and drink - Stay away from too much caffeine, sugar and food that makes you sleepy (like turkey which contains tryptophan). Getting a stomach ache, the shakes or dozing off during the test will likely effect your performance.
Day of the Test
Dress in layers - Make sure you are dressed comfortably for the test. Since the temperature of the test center can be quite unpredictable, be prepared by wearing clothes that can either be added or removed quickly. Sweating profusely during an exam or shivering uncontrollably will certainly effect your performance.
Bring supplies - Be prepared by packing extra pens, pencils, tissues, a clock (make sure it's silent), water, medicine in case of a headache or stomach ache and your favorite good luck charm.
Arrive early - Arrive at the test center extra early so you can get settled, adjust to your surroundings and start to focus on the test. There is enough stress associated with the test itself, so try not to add any more stress by leaving only minutes to spare. Assume that something will go wrong on your trip to the test.
Taking the Test
Bring your admission ticket and your identification - You need these items in order to take the test so please don't forget them. Tape them to your forehead the night before if you have to.
Try to spend 1:36 per question - If you spend roughly one minute and 36 seconds on each question, you will have enough time to finish each question. If you find you're spending too much time on a question, move to the next one. Don't forget - each question is weighed equally.
Answer every question on the test - Even if you are running out of time, make your best educated guess on those questions. Don't forget - you get points for each question answered correctly and are not penalized for incorrect answers. Let the rule of odds help you get the highest score possible.