You are not asking the right question. How can you go after parallelism first if there is no question of parallel elements? I could say "singular versus plural," which is the most common difference in answer choice that you can exploit but what if that is not part of the question you are attempting?
The simple answer is that you should make the decision that is clearest to you and that makes on answer choice right and one wrong.
A couple of things about what you have mentioned:
1) Word choice can be about style, such as the difference between "maybe" and "could be" I would never want to attack that first. But word choice could also mean grammar such as verb tense and this would be something good to go at if you are confident in that aspect.
2) You mentioned parallelism. I have noticed that as you get to the higher scoring questions the difference between the final two of three choices on most questions is parallelism. Still this is not usually as obvious as other possibilities so you might end up narrowing the choices with something else first and then investing the time that is needed to confirm parallel elements.
Here is an article I wrote describing why you should use you best decision point first.
Watch out for Zombies... in Sentence Correction!
A few years ago, vampires were big in popular culture. A certain teen vampire series sold millions of copies and had people of all ages worked up about the virtues of vampires. But now people seem to be moving away from vampires in the direction of another, more sinister type of monster - zombies! Several new movies and even a new television show featuring these creatures have appeared recently. Perhaps these screenwriters are trying to help you improve your sentence correction?
What precisely is a "zombie" and what does it have to do with sentence correction? According to West African tradition, a zombie is a person that has come back from the dead to walk again. In that tradition a zombie is usually controlled by a powerful sorcerer. In the last several decades, the zombie concept has been appropriated by American culture and has been used in a variety of different stories. But one thing remains the same in all zombie stories - zombies are always up to no good! Zombies never come back to clean your house or do a little gardening. They always want to harm you and they are always dangerous!
A "Zombie" in sentence correction is an answer choice that you have eliminated for a good reason, but that you bring back to life later on as you are working through the question. For example, you will notice that a particular answer choice uses a singular verb when a plural verb is necessary and so you correctly eliminate that choice. Then as you evaluate the remaining choices, you find that none of them sounds good to you and so, in desperation, you return to a choice that you have already eliminated. In the best case scenario you simply wasted some of you valuable time re-evaluating this choice and you conclude, again, that it is incorrect. In the worst case, you convince yourself that this is the best choice and you answer incorrectly. But whatever happens, these sentence correction zombies are here to do great harm to your GMAT score!
Try this question that I adapted from the Veritas Sentence Correction 2 book:
"Featured in circuses for more than a century, trapeze artists perform acrobatic maneuvers while hanging by the ankles from swings, rebalancing so frequently that spectators see only his continuous fluid movement.
(A) trapeze artists perform acrobatic maneuvers while hanging by their ankles from swings, rebalancing so frequently
(B) trapeze artists perform acrobatic maneuvers while hanging by their ankles from swings, rebalancing frequently enough
(C) trapeze artists use their ankles to hang from swings, perform acrobatic maneuvers, and rebalance so frequently
(D) the trapeze artist hangs from swings by the ankles, performing acrobatic maneuvers and rebalancing so frequently
(E) the trapeze artist hangs from swings by his ankles, performs acrobatic maneuvers, and he rebalances frequently enough
The first the thing that you might notice is the 3/2 split between "trapeze artists" in choices A, B, and C and "the trapeze artist" in choices D and E. This is a classic singular versus plural "decision point." Now that we have identified a decision point we look to see if there are clues in the sentence that will help to make the choice. In this case we have "his continuous fluid movement" at the end of the sentence. The pronoun "his" is part of the sentence that does not change. Therefore we know that the antecedent to this singular pronoun must also be singular. So "the trapeze artist" is correct. Answer choices A, B, and C are eliminated.
Evaluating Choices D and E we find that the list in choice E in not parallel. The trapeze artist "hangs..., performs..., and he rebalances..." The "he" ruins the parallelism of the list. Choice E also uses the unidiomatic phrase "he rebalances frequently enough that spectators see only..." however, idioms can be tricky and if another option is available it is often better to leave the idioms for last.
What about Answer Choice D? Is this a sentence you would have written? "Featured in circuses for more than a century, the trapeze artist hangs from swings by the ankles, performing acrobatic maneuvers and rebalancing so frequently that spectators see only his continuous fluid movement." Many students find this sentence to be awkward, even mildly unpleasant. Something about a sentence that sounds this strange makes students doubt themselves and return to the other choices. Suddenly Choice A does not seem so bad. There is even the subtle difference between Choices A and B, where B has "rebalancing frequently enough" that we know is unidiomatic. It would not be difficult for a test taker to be convinced to go with Choice A and to think that he or she was clever for choosing the proper idiom, forgetting that a minute ago Choice A was conclusively eliminated due to a solid singular-plural decision point.
This is why it is so important not to reconsider answer choices once you eliminated them. NO ZOMBIES! When a choice is gone, it should stay gone. Here is a process to help you with that:
Process of Elimination
Sentence Correction is a process of elimination and you have to be able to trust that the answers you have eliminated are indeed incorrect. This is the key to efficient and accurate work in sentence correction. It does not matter how you eliminate choices, whether you know that something is a relative clause that does not modify the noun immediately preceding it or whether you simply know that this word used in this location does not sound right. Whatever method you use you need to be confident and not second guess yourself.
The best way to be confident in your decision to eliminate an answer choice is to make your first eliminations based on your best decision point first. Great decision points have a definite right and wrong answer: Singular/ plural, verb tense, and misplaced modifier, are examples of decision points that have a right answer and, more importantly, a wrong answer. A Great decision point is also one that you are confident in using. It may be the case that a particular idiom is right and another wrong, but it does not help if you do not know which is which.
Avoid Zombies
1) Use your best decision point first. There are often multiple differences between the answer choices on a single sentence correction problem. Because you are not going to re-evaluate an answer choice once you have eliminated it, it is important that you use your best decision point first. This means a decision point that is a choice between two alternatives where one is right and the other is wrong and you are confident that you know which is correct.
2) Always keep track of your eliminations. On sentence correction a simple A - E on your scratch paper can help you know which choices are eliminated so that you never bring them back as Zombies.
3) NO Zombies! Once you are used to the fact that answer choices that have been eliminated stay eliminated you can avoid those troublesome Zombies. And if you really do not like the way an answer choice sounds you can quickly remind yourself of the reasons you eliminated the other choices.
Vampires might be teen heartthrobs and they can even help you with your sentence correction, but Zombies are never attractive and never helpful. Luckily, if you stay alert you can avoid Zombies on the GMAT if not at the movie theater.
