Strategy is king on tests like the SAT, GRE or ACT. After preparation, the most important thing to getting the highest score is to develop a strategy long before you take the test. The reason for the importance of strategy is that these tests are timed.
What changes when a test is timed? What changes is there is a premium on answering as many questions as possible within the time limit. This means you loose points for thinking about a problem more than a few seconds. Because of this, you cannot afford to take any question personally; you need to assign a time limit on each question and if you cannot answer the question within the time limit, you need to either guess the answer or leave it blank and continue to the next question. Whether you guess or leave a question unanswered depends on how the standardized test will be graded, and you need to be thoroughly familiar with that grading policy.
Taking a standardized test is like running in a race. If you stumble you need to get up and continue on the race. You cannot allow any problem to prevent you from finishing that race.
Of course, unlike a race, after you complete a standardized test you may have the opportunity to return to certain questions and answer them a second time. If that is permitted, then you should take notes during the test on which questions you guessed on or left blank so you can quickly return to them and perhaps re-consider your answers after you finish.