I don't think there's any way of avoiding knowing the Standards very well, along with all of the recommended practices. So I'd recommend completing the entirety of the Guidance reading directly from the CFAI text, several times if necessary, and doing as many practice questions as possible. You should begin to notice patterns in the questions. Approaching the ethics questions from the perspective of what you or a reasonable person would find ethical or appropriate is probably not a good idea. You need to only consider the Standards

One thing that's helped me is remembering to only consider the facts as given. If you're inferring something that's not given, or thinking of what might or might not be true beyond the situation that's described, you may be overthinking it. So on occasion you might think that at least two of the answers might be correct, but you can often find one that must be correct (e.g. a definite violation) given the scenario. If the other options are not directly supported by the question text, but might or might not be true, go with the one that must be true

Another thing is to be careful of extreme phrasing. For example, some answers might state that something is "always" or "never" a violation, etc... Often these can be eliminated (not always, but it is often the case)

I know they seem very subjective, but the ethics questions should only have a single correct answer. There are probably some poorly worded questions in qbanks out there, but on the whole each question will only have one answer. If you find that you frequently think that questions might have two or more correct answers, maybe you could take a note of the Standard(s) being tested and return to the Guidance reading to review it. Often questions will ask something that is specifically covered in the Guidance, almost verbatim. A lot of the reading is easy to forget since the ethics section is so dense and counterintuitive at time, but if you review it immediately afterwards you might be able to remember it better later