Distinguish debatable claims from facts and matters of pure taste, then choose one debatable claim to argue for the rest of the unit.
A debatable claim is one reasonable people could disagree about, backed by reasons and evidence -- not a fact, which is already settled and provable, and not pure taste, where no evidence could change anyone's mind, like a favorite flavor.
Test any claim with a question: could someone reasonably disagree, and could evidence help settle it? If yes to both, it is debatable and ready for an opinion essay.
Mastery looks like: They correctly sort claims into fact, taste, and debatable, and choose a genuinely debatable claim to argue for the unit.
Common stumbles: Choosing a claim that is really a settled fact or a matter of pure taste; picking a claim so one-sided that no real counterargument exists.