I am no longer an aspirant. However, I qualified the Civil Service Exam in 2016 with History as my optional.
The most difficult aspect of the history optional is the vastness of the syllabus. This renders revisions very difficult and time consuming. The best way to approach the subject is to
- Start Early
- Refer the Standard Textbooks.
- Develop a cursory understanding of the topic before you delve into details ( Books like Survey of Indian History by KM Panikkar can help with this.
- Selectively refer IGNOU Texbooks
- Start preparing Maps early on.
- Refer previous year question papers and attempt to write the answers and get them corrected.
History, even though vast, is a highly rewarding and joyous subject to learn. All the best to you.