In the last 4 months you should focus on the topics which carries more weightage in the exam. 

You should revise your syllabus properly and focus on the current events which are happening. Read newspapers daily like The Hindu and The Indian Express. You can also watch news regularly including NDTV, BBC and CNN channels

It is important that you clear your concepts and work on time managenent. Solve Mock test series for your practice it will also help you to analyse your preparation level. Always try to learn from your mistakes and try not to repeat your mistakes. 

All the Best!!