I seem to get must be true, inferred, main point questions wrong the most. Are there any efficient ways to go about this?
must be true = cannot be false (I know that's obvious, but sometimes that formulation helps clarify what you're supposed to be looking for.)
Most "must be true" questions are looking for an assumption (assuming you're talking about the arguments section and not the games section). An assumption is just an unstated premise. "Must be true" assumptions are assumptions that, if they are untrue, make it so that the premises given don't work together to reach the conclusion. So, pretend te nswer choices aren't true and see if the argument still works. f it does, eliminate the answer choice. If you mean "must be true" for the logical games section, first look at any previous work. Then, instead of plugging in the answers and seeing which one is true in every case, set up scenarios where the answer choice is false/not the case. If you find even one instance of it being false and the "puzzle" still works, then you can eliminate it.
The answers to "inferred" question stems can always be grounded in the text. They aren't asking you to make anything up. You should be able to say something like "because X (some line from the text), it must be that Y (some answer choice.)"
Main point questions can be a pain. The most common mistakes are choosing answers that don't include enough about the passage. Be careful of answers that address some aspect of the passage but not the whole thing. You should be able to narrow it down to 1 or 2 choices, see what is different about them, and see how that difference makes one of them wrong.