Any quick tips for dealing with Necessary Assumption Questions?

Yes! Let's start with these three:

1. The necessary assumption is a piece of evidence that the argument needs but does not have. The right answer has to be something that fills in a blank within the argument - some place in which the arguer didn't provide you with the evidence, but instead just assumed that the evidence was true.
2. To identify that place, look for shifts in language: Is there some place in the argument where the author changes the subject? If the author provides evidence about one thing, and a conclusion about something else, that author has assumed there's a connection between those two things. That shift in language gives evidence of the shift in logic.
3. The right answer is necessary. That means that if you take it away, the argument will die, right? When you think you've found the right answer, ask yourself this question: "If this answer choice weren't true, would the conclusion still make sense?" If the conclusion can live without the answer choice, it's not the right answer! If the right answer isn't true, then the conclusion of the argument will become stupid. This is because the conclusion depended on the truth of the right answer.