Devising a smart test prep strategy
Which test should you take?
The SAT and ACT are two very different tests that are designed to test different things. The best way to figure out which test to take between the SAT and ACT is to try both beforehand. Most test prep companies offer free practice tests with no further obligation to sign up. There are some that even offer "hybrid" tests that have questions from both exams and project your likely scores on each test. At the very least, you can try the free practice tests on-line that are offered by Collegeboard.com and Act.org. Go with which ever test you do best on and that you feel most comfortable with.
When should you take test?
I recommend that you take the SAT or ACT for the first time in the spring of your junior year. You should allow at least 8-10 weeks prior to the test to study. I mean actual studying, not just buying a book and then opening it up once or twice before the test. I'm a huge proponent of organized test prep, not just because I do this for a living, but because for many students, it actually works. Ultimately, no matter what route you take, however, there's no substitute for practice. Simply put: if you practice your scores will go up; if you don't, they won't!
How many times should you take the test?
Ideally once, but more realistically twice. Generally, scores start to level off and you start to really hate the test (which doesn't help at all!) if you take it more than three times.