Developing a holistic understanding of both political theory and international relations topics within the PSIR syllabus requires a systematic and comprehensive approach. Here are some steps to help you achieve this:

1. Familiarize yourself with the syllabus:
- Start by thoroughly reading and understanding the PSIR syllabus provided by the UPSC.
- Identify the key topics and sub-topics within political theory and international relations.

2. Read textbooks and reference materials:
- Consult standard textbooks recommended for PSIR preparation. Some popular ones include "An Introduction to Political Theory" by O.P. Gauba and "International Relations" by V.N. Khanna.
- Read these textbooks chapter-wise, making notes of important concepts, theories, and case studies.
- Supplement your reading with reference materials such as scholarly articles, research papers, and reports from reputable sources.

3. Follow current affairs:
- Stay updated with current events and developments in the political and international arena.
- Read newspapers, magazines, and online sources to understand the practical application of political theory and international relations concepts.
- Analyze the events from different perspectives, considering the theories and frameworks you have learned.

4. Engage in critical analysis:
- Develop the ability to critically analyze political theories and international relations concepts.
- Evaluate the strengths and weaknesses of various theories and their applicability to real-world situations.
- Practice connecting theoretical concepts with practical examples to enhance your understanding.

5. Participate in discussions and debates:
- Engage in group discussions or join study circles to discuss political theory and international relations topics.
- Sharing and exchanging ideas with fellow aspirants can help broaden your perspective and deepen your understanding.
- Participate in mock debates and model United Nations simulations to apply your knowledge and gain practical experience.

6. Solve previous years' question papers:
- Solve previous years' question papers to familiarize yourself with the exam pattern and the type of questions asked.
- Analyze your performance and identify areas of improvement.
- Revise and strengthen your understanding of the topics based on the feedback received.

Remember, developing a holistic understanding of political theory and international relations requires consistent effort, dedication, and a multidimensional approach. Regular revision, self-assessment, and seeking guidance from experienced mentors can further enhance your preparation.