There are several ways to improve on this topic:
1. GMAT Courses & Tutoring Worldwide:
http://www.800score.com/gmat-courses.htmlClearly, tutoring is the most efficient way. A professional, who can see where you're struggling, will provide the best guidance.
2. GMAT prep guide:
http://www.800score.com/content/guidetc.htmlThe prep guide is very handy and can give you an insight on the specific unclear moments in solutions.
3. Practice in solving.
http://www.800score.com/download.htmlhttp://www.800score.com/forum/Break questions into simpler concepts and you'll see which concepts you do understand, and which ones you don't. Keep you head up and start from the simplest questions and concepts, then move on to the hardest ones.
Of course, the combination of these options & your personal effort will give you the best results.