I found this on Manhattan GMAT
's forum while searching for an answer:
-Read the original sentence all the way through.
-If you happen to spot anything problematic, examine. If it's an error, cross off A. Then scan the other choices vertically, at the same point as that error you found (do NOT read the whole answer choice), and cross off any others that repeat the same error.
-Repeat the above until you've dealt with everything you happened to see on your first read-through of the original sentence (note: sometimes you won't see anything on the first read-through!).
-If you've exhausted the original sentence, do a vertical scan of the first word of each choice. If you can identify the potential error based on the differences you see, deal with it. If not, do a vertical scan of the last word of each choice - same thing.
-After that, do a vertical scan starting at the beginning of each choice. If you notice a difference when scanning but you don't know what error that difference might signify, keep going - look for a different split.
-If you've dealt with everything you know how to deal with and you still have more than one choice left, pick something and move on. Don't agonize over it - just pick and go.
by StaceyKoprince. (minor editing mine)http://www.manhattangmat.com/forums/a-h ... -t732.html