Studying ancient India by R.S Sharma book in one day is not an easy task, but it is possible with the right approach and strategy. Here is a guide on how to do it:

1. Create a Study Plan
Create a study plan for the day and allocate time to each chapter of the book. Divide the book into manageable sections so that you are not overwhelmed. Plan breaks to avoid burnout and fatigue.

2. Focus on Key Concepts
Focus on the key concepts of each chapter. Identify important dates, events, and personalities mentioned in the book. Make notes of key concepts and important information for later reference.

3. Use Visual Aids
Use visual aids such as maps and diagrams to help you understand the geography and architecture of ancient India. This will also help you to remember important information.

4. Read Critically
Read the book critically and actively engage with the material. Ask yourself questions such as "why is this information important?" and "how does this relate to other concepts in the book?"

5. Memorize Important Information
Memorize important information such as dates, events, and personalities. Use flashcards or other memory aids to help you remember this information.

6. Test Yourself
Test yourself on the material you have studied. Use practice questions and quizzes to help you identify areas where you need to improve.

7. Revise and Review
Revise and review the material regularly. This will help you to consolidate your knowledge and ensure that you remember important information.

90 Day Study Plan for History for UPSC CSE Prelims
If you have more time to study, here is a 90 day study plan for history for UPSC CSE prelims:

1. Day 1-30: Ancient India
Study ancient India using R.S Sharma book. Focus on key concepts, important dates, events, and personalities.

2. Day 31-60: Medieval India
Study medieval India using Satish Chandra book. Focus on key concepts, important dates, events, and personalities.

3. Day 61-90: Modern India
Study modern India using Bipin Chandra book. Focus on key concepts, important dates, events, and personalities.

In conclusion, studying ancient India by R.S Sharma book in one day requires a focused and strategic approach. Creating a study plan, focusing on key concepts, using visual aids, reading critically, memorizing important information, testing yourself, and revising and reviewing regularly will help you to achieve your goal. For a more comprehensive study plan, consider the 90 day study plan for history for UPSC CSE prelims.