Here are some tips for what you should DO to help improve your test scores:
1. Register Early for the Tests in Your Area.
It is not uncommon for popular test sites to get booked fast, so do not wait until the last minute to sign up for the required standardized tests (usually SATs). If you can take one during the spring of your junior year and one in the fall of your senior year, that may be to your advantage. You will often have the option of dropping the lower score or at least showing improvement on the second effort.
2. Select a Good Book to Study for the Standardized Tests.
Select a book that has practice tests in it and that is current—as in published at least annually. I would encourage you to take any test that you can take more than once, if the lowest score does not count against you.
3. Learn How to Study for Tests.
In general, a good way to study for tests—especially verbal tests like spelling, history, vocabulary (and some fields in science)—is to write the answer on one side of a sheet of paper and the question on the other side.
For example, you could write the definition of a word on one side, and the word on the other. You could write the answers to questions that you commonly get wrong, like spelling words, math theorems, or sequences of presidents, over and over again until your hand commits the correct answer to memory. The process of writing something will work for those who are kinetic and visual learners, because you get to see the words and feel them.