1. One should start by checking the syllabus and the last five years question papers in a comprehensive manner. 

2. Newspaper reading is very important.    – The reading should be complemented by Atlas, by seeing relevant political and physical locations of places in the news.   – One should also see the meaning of economic terms on the internet.   – International and Government institutions, statutes and other bodies, their headquarters, ministries etc should also be seen on the internet.The depth up to which Newspaper should be read could be gauged by seeing the last five years question papers. 

3. Basic NCERT Texts from Class 9th to class 12th of subjects History, Geography, Polity, Economy, Society, and others. These days the questions are coming directly from NCERT, so it’s relevance is increasing. 

4. Apart from this, some books like Laxmikant, G.C.Leong, and Spectrum should also be thoroughly completed. 

5. For other topics like security, disaster management, etc. one should refer to coaching magazines.

6. Repeated revision of the material is very crucial for mains, then only the relevant points would be recalled during the mains exam. For prelims, the key is solving good amount of test paper to find one’s optimum level of the question’s to be attempted, so that score could be maximized. 

7. These are material sources that would add to Knowledge base, but one needs skill set to crack the exam. 

8. For the skill set, I would suggest the prelims test series of any good coaching institute and revising the solved paper at least twice. 

9. For mains daily answer writing is the key. Completing the paper within the stipulated time period is the most difficult task. One could compromise on quality but quantity ie completing the paper is paramount. 

10. Most important ingredient that is required is the right guidance, dedicated study and perseverance to face the struggle and to keep improving.