Know what you are going to write, even before you see the prompt - Part 1: Structure.
First of all, come up with an essay STRUCTURE that you will use, no matter what the prompt is, no matter what your examples are. You should not be trying to organize your paper while the timer is counting down, so do it now. Many different formats might be appropriate; here's a suggestion that is based upon the 5-paragraph essays that you're already writing in school.
We'll discuss the overall paragraph structure first:
Introduction (1-2 sentences)
Example #1 (6-8 sentences)
Example #2 (6-8 sentences)
Counterexample (6-8 sentences)
Conclusion (1-2 sentences)
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