Hi hotdream,
That approach to CR will definitely not work. Often, the wrong answers will be very closely related to the argument. They just don't relate in the right way. For instance, on a Strengthen the Argument question, some of the answer choices may weaken the argument. If we dismiss them as irrelevant, then we haven't understood the argument well enough.
As far as I'm concerned, taking the time to fully understand the argument is the only way to go. If you're working on an assumption-based question, you want to go into the answer choices with a clear sense not only of what the conclusion and premises are, but also of why the author thinks the premises lead to the conclusion. Ideally, you want to identify one or more assumptions up-front, too (what is the author overlooking?), but if you can't find anything, it's okay to jump into the answer choices.
On an inference/conclusion question, there's less up-front work to do. The given statements may work together to create some larger conclusion, and if this is the case, you want to identify that. However, often the correct answer will just be some random statement that is supported by the statements above.
In any case, eliminating answers that are unrelated to the argument is never *wrong*--clearly those answers won't work. It's just that that kind of elimination alone is not sufficient to get you all the way to the right answer on most CR problems.