In order to start your preparation for UPSC you should be aware of the syllabus. You can also refer previous year papers to understand the exam pattern and level of questions. You should focus on GK as well for that you can read newspapers. Give proper time to revision. 

For UPSC Preparation you can follow below books

For Prelims: Art and Culture : NIOS material / Nitin Singhania notes History Ancient - R. S. Sharma History Medieval - Satish Chandra History Modern - Bipan Chandra Additions for Mains: History India Since Independence - Bipan Chandra History World - Arjun Dev Additions for optional: The Wonder That Was India – A.L. Basham Ashoka and the Decline of the Mauryas – Romila Thapar Medieval India: From Sultanat to Mughals – 1- Satish Chandra Medieveal India: From Sultanat to Mughals -2 – Satish Chandra Mastering Modern World History – Norman Lowe.

All the Best!!