It is high time one seriously starts solving previous year question papers to get a strong hold on the syllabus and get much needed confidence.
Previous year GS papers have some good questions on Modern History, Polity, Economy and Geography section and solving them will help get a broad idea about many topics.
There are very few books available on Mains GS solved papers. One good book is from Arihant publications. Reviews on Flipkart and Amazon are good.
Good thing about this book is, it has chapter wise solved papers. It makes your job very easy. You can just focus on topics relevant to present syllabus.
Fortunately it is available on Amazon India (Not on Flipkart). Buy the book for question papers. Model answers may be good, but they should be read to get a rough idea about approaching the question.
Now available on Amazon. To go there,click here.
In case your optional is Political Science, they have a similar book for it. It is available on Flipkart. Click here.