From what you’re describing, it sounds to me like what you could use is more familiarity with the specific flaws that are heavily tested. The flaw/assumption similarity that you describe is one type of way in which an argument can go wrong, and it sounds to me like that’s one that you’ve either learned very well, or that is just naturally intuitive to you. When you familiarize yourself with a handful of others (maybe 8-10), you should have a quick grasp of what’s going on with the more specific ones. For instance, there are certain phrases that signal a cause and effect conclusion when it’s not warranted by the evidence, like, “This shows that X can result in Y.” Once you realize it’s a cause and effect flaw, there aren’t that many ways in which the answer choice is offered – typically, it will be in either general terms (“infers a causal connection from a mere correlation…”), or it will offer you a specific alternative to the asserted cause/effect: “fails to show that Y may cause X.”
That’s one example from a variety of flaw types, but the good news is, there aren’t that many of them that show up often. The more you do (and ask questions about), the more you’ll recognize them when you see them. A big part of the improvement process is gradually seeing fewer trees and more forest.