In an objective paper, time management matters as much as knowledge. A reliable approach is two passes: go through the paper once answering everything you are confident about, skipping the rest, then spend the remaining time on the harder questions with the easy marks already banked.
When you are down to two options, read the question again before choosing. A large share of wrong answers come from misreading the question rather than not knowing the material - particularly questions containing 'not' or 'except'.
Avoid changing an answer at the last minute unless you have found clear evidence you were wrong. First instincts are usually right when the material has been studied properly.