GS4 Approach

For ethics my approach was simple. I started by reading Lexicon (pick any standard book), then I tried to understand the meaning of every term mentioned in the syllabus. I tried to incorporate examples, case studies, ARC recommendations and comments in my answers.

Sources

• Lexicon - should be a good starting point, also only a quick read
• Vajiram Notes - mainly for philosophy part 
• Google - followed this widely suggested approach and put together definitions topic wise and also read up on philosophy part
• Applied ethics - This here is a great website to cover applied part. Alternatively, you can find summaries of the same in my notes linked below.
• Examples and Anecdotes - came up myself for some and took them from a brilliant compilation by Mr. Abhishek Surana Sir whose blog you can find here.

MY COMPLETE ETHICS NOTES

Case Studies

I followed certain frameworks that helped me quickly start writing after having read and understood the case. 

• Introduction variations - Stakeholder diagrams, Moral / Ethical dilemma illustration, Facts of case
• Conclusion - quote by famous personalities or Bhagavat Gita, SWOT analysis for any decision made

Some of my answer scripts

Ethics copy (refer for Part A)
Ethics copy (refer only for Case Studies)

Despite being adequately prepared and my relative comfort with ethics paper, I did make a strange mistake in my actual exam. Be it due to the time crunch (especially an issue in GS4) or exam panic, I had goofed up my last case study on Edward Snowden - who I actually admire but ended up presenting a view against. In essence, try and mentally practice more case studies (no need to actually write them down) - helps in thinking quickly and with clarity.