1. Don't wait until the last minute to do a practice test.
The SSAT is much like any other standardized test. You will be more confident if you take a couple of practice tests. Practice tests give you a better understanding of the test format, the kinds of questions which are asked and the time limits involved. Purchase the widely available test preparation books and CD's at least a year before you plan to take the test.
2. Don't wait until the last minute to remediate learning deficiencies.
For example, suppose that you are sort of weak in math. It makes great sense to remediate that deficiency as soon as you can. Get extra help. Hire a tutor. There are plenty of online sites which will give you lots of extra practice. But start as early as you can. Practice as often as you can, preferably daily, until you are really good at the skills required.
3. Don't arrive late for the test.
Test centers generally service many candidates. Be early. Read the rules about what you can and cannot bring into the test room. "I didn't know" is not an excuse. Arriving on time gives you time to gather yourself together, visit the rest room, eat that power bar you brought with you and calm your nerves.
4. Don't even think about cheating.
You may think that you can beat the system. Don't try it. Your future is at stake. You simply don't need a blot on your file, do you?
5. Don't worry about your score.
Remember that the SSAT scores are only one part of the picture which the admissions staff looks at. If you are a really good lacrosse player or play an instrument to a high standard, the admissions staff will consider those aspects of your file very seriously. Just show the school that you have put forth your best efforts and that you are determined to succeed.
SSAT's are a good introduction to the real world of assessment. The next test you will most likely encounter is the SAT which is used by most colleges and universities to assess your readiness for tertiary level academic work. After that LSAT's, GMAT's and so on are part of your adult life.