What are you using so far? Do you have a book that's teaching you the grammar and meaning issues that are tested by the GMAT? If not, you'll want to get something that helps you with that.
Note that I'm talking about something that will teach you what to do, not just give you practice problems. For practice problems, use the OG (official guide) books.
Since you asked, we do have a Sentence Correction Strategy Guide - and I feel comfortable saying that it is consistently rated the best SC book on the market. But don't just take my word for it - I'm biased. :) Go look at what's available and ask other students what they use and like, then decide for yourself!
Here's an article to get you started (general process for all SC questions):
http://www.manhattangmat.com/blog/index ... n-problem/And here's another about how to study SC:
http://www.manhattangmat.com/articles/GMATprep-SC.cfm