Totally Struggling in SC

It takes time to improve SC... especially if your grammar and english skills are weak. You have to start with Structure of sentence, first master this. You should be able to tell the difference between a run on and a proper sentence. This is KEY, without this you will have a lot of trouble trying to figure out how to fix modifiers and missing verb issues. If you understand this first aspect then you can eliminate a lot of wrong choices just because they are not complete sentence.

Once you've mastered this simple aspect then move onto Subject verb agreement, this is again very easy to learn and spot. Easy points, then move onto Tenses, which are not tested heavily but you need to know this to make sense of sentences. Then onto Pronoun issues. These appear quite often and very easy to learn. Then next step is to learn modifiers, ing vs ed modifiers and how to modify the correct thing. Then onto comparisons. Last but not least you have to learn to see what words are redundant, and learn idioms.

Idioms by themselves will not help! Many wrong choices have correct idioms so you will pick the wrong choice if you only go by idiom. Hope this helps! It took me several weeks at the minimum to get this down, and I am a native speaker.... So don't underestimate SC.

Good luck! & Also Give E-GMAT a try, very good course and I used it to improve a lot. Manhattan itself i not sufficient for non-native speakers.