I have no idea what MLSAT says, but here's what I do.
The first person generally presents a full arguments: premises + conclusion. You want to identify the person's conclusion. The second person may say something that clearly expresses disagreement ("Your reasoning is absurd!"), thereby concluding the opposite as the first person, or may conclude something different entirely, or may have no clear conclusion at all. You want to identify what the second person is doing.
For example, here, Elaine's conclusion is the second sentence, marked with a "therefore," and Frederick's argument is nothing but conclusion.
Next, you want to identify the most obvious point of disagreement. There may be more than one point of disagreement, but you want at least the most obvious one.
Here, probably the most obvious point of disagreement is whether museums should collect only the works of recognized masters (F's conclusion) or the best artworks from each period and genre (E's conclusion).
Once you've got that, go into the answer choices. You want to identify which person would definitely agree with the statement, which person would definitely disagree, or if you just can't tell from the info provided. I tend to mark this as
or ?. You want one to agree and one to disagree in order for the answer to be right; that's a
Here, in A, we don't really know what either one thinks. E says that the best artworks may not be recognized by experts as masterpieces, but that doesn't necessarily mean that they are
masterpieces; they're just the best artworks. F never touches on the issue of masterpieces. That'd be ? and ?.
In B, E definitely says this (this was her conclusion), and F definitely says that museums should do something else. This would be
. (This was the disagreement that we identified at the outset. If you're lucky, that will happen. If you're not lucky, that won't happen, but it's worth checking for anyway.)
In C, both agree with this. This would be
In D, this issue is never addressed at all. We don't know what either thinks about this. This would be ? and ?.
In E, same problem as in A. "Masterpiece" isn't quite handled in this way in either argument. That'd be a ? and ?.
What you want is a
, so B is the answer.
After you've got that approach, drill and review like crazy. It'll click.