A good checklist for each question comes from popew626:
Subject-verb, tense, modifier, parrallelism, comparison, and idiom.
If you run through that checklist each time looking for things that are wrong with each answer, it should help you narrow it down to the right one.
Also, remember Occam's Razor: don't go looking for the complicated answer when the simple one will suffice. In other words, sometimes the answer is A. Don't over-correct. And if two answers are grammatically correct, usually the one with the more simple or elegant structure is the correct one.