The way I usually tackle SC questions is as follows:
1) Line the responses up and see where they differ.
2) Take each response in turn, and examine the differing portions for errors.
3) When you find an error in a response, eliminate it.
4) Repeat until only 1 answer remains, and check to make sure it has no errors.
This is the gist of how I approach SC questions, and I find that it works well for me. After enough time spent preparing for the GMAT, you'll eventually have seen enough SC questions to be able to identify the kinds of rules that the GMAT is testing for. Once you've reached that point, eliminating SC answers will take fairly little time, and you should be able to handle most questions in a minute or less.
Hi, I'm DonQuixote, a former GMAT Pill student who scored 780. I'm very grateful for this score and have now joined their staff My account of my GMAT experience can be found here.