First, understand how the test works. Some tests penalize you for wrong answers, some do not. If there are no penalties for wrong answers you want to answer every question, even if you have to guess. If there are penalties, you don’t.
Second, don’t fixate on individual questions. Go through the test for start to end, answering every question for which you are certain, and skipping those for which you aren’t.
Third, go back and review the questions you skipped. It’s actually pretty common that the answer to one question is in the text of a later question, or a later question will remind you of the answer to an earlier one. Again, on this pass, don’t spend too much on any one question.
Then, go back to the questions you still haven’t answered, and decide which of them to invest your remaining time on.