As you can see there are periods of correlation and diversion. In my view, it depends on the issue. Let’s of there is a big event in the US you can observe it impact of the US Indices and then take a call on how the Indian indices will react. There are global events during which the markets will act in unison. You can see that during the 2007-2009 the global financial crisis all the major markets crashed alike. It is always a good idea to keep track of the major gloabl indices such as US, Japna and Major Eurpoean indicies. Gives you an idea of the factors affecting them and the likely impact on ours. But you will have to filter out the irrelevant stuff, which comes from experience and knowledge.
Tradingview charts, WSJ, NYT, Marketwatch, The Economist, Marketrealist, Yahoo Finance, Bloomberg are some places you can look at.