Law as optional subject has come in limelight in recent years and many non-Law background candidates have made it possible to crack this examination with Law as optional subject.
Even, in Civil Services Examination 2013, Law has given highest success-rate among popular optional subjects.
Law is specialized theme and is logical in nature. If you look at the syllabus, a part of it gets covered while preparing for Main Examination - General Studies Paper II.
Try if you can understand it with self-study. But, for some portion, you need to take help as you have to compete with Law background candidates and have to develop answer-writing skills so that you meet examiner’s expectations.