Books serve as the basics and choosing the right set of resources is essential to crack the exam.
You may find, that the syllabus covered is similar in all books, but the treatment and application of content decide the best books.
Here are some best selling books for General studies in Preliminary. Choose your optional subjects,based on the availability of suitable study resources.
NCERT Text Books from Class 6 – 12 serve as the basics for any competitive exam
For General Studies, all of them are great resources.
General Studies Paper 1 Manual by Pearson
General Studies Paper 1 Manual by McGraw Hill
General Studies Paper 1 Manual by Arihant
General Studies Paper 2 Manual by Pearson
General Studies Paper 2 Manual by McGraw Hill
General Studies Paper 2 Manual by Arihant
Current Affairs
India Year Book
Manorama Yearbook.
For CSAT (Aptitude)
Verbal & Non-Verbal Reasoning – R. S.Aggarwal
Cracking the CSAT – Arihant
Analytical Reasoning – M. K. Pandey
I recommend you develop the habit of making notes and reading magazines.This will help you to attack the questions on current affairs.
In addition to all the above points, a mentor can help you to keep you on track every now and then. In fact, one of my cousins had taken coaching from one of the best IAS academy in Chennai and cleared the prelims successfully. They have an expert faculty team, in-house study materials with good teaching methodologies, test series and Mock test.
My advice would be to use the available time and resources in the best possible manner. You will come out with flying colours.
All the best.