Studying previous year's papers of the UPSC (Union Public Service Commission) is an essential part of your exam preparation strategy. The timing for studying these papers can vary based on your study plan and the stage of your preparation.

1. Initial Stages of Preparation:

1. In the early stages of your preparation, focus on building a strong foundation    in the subjects and topics outlined in the UPSC syllabus. Spend more time on understanding concepts, reading standard textbooks, and gathering study materials.

2. You can start with previous year's papers as a reference to get an idea of the exam pattern and the type of questions asked, but don't dive deep into solving them at this stage.

2. Midway Through Preparation:

1. As you progress in your preparation and cover a substantial portion of the syllabus, consider incorporating the study of previous year's papers.

2. Begin by solving papers from the past 5-10 years, focusing on the General Studies (GS) papers, as these are common to all UPSC exams. This will give you a better understanding of the evolving trends in the exam.

3. Mock Test Phase:

1. As you approach the final months before the exam, incorporate previous year's papers into your mock test practice. You can start by taking full-length mock tests that simulate the actual exam conditions.

2. Analyse your performance in these tests, identify your strengths and weaknesses, and revise accordingly. Solve more previous year's papers to further fine-tune your preparation.

4. Last-Minute Revision:

1. In the last few weeks leading up to the exam, focus on revising and consolidating your knowledge.

2. Solve a few more recent previous year's papers to boost your confidence and get a final feel for the exam format.

5. During the Final Week:

1. In the days just before the exam, you can do a quick review of key concepts and solve a couple of more recent papers to keep your mind sharp.

2. Avoid studying new topics or attempting too many papers during this period to prevent burnout.