When to introduce caching in your api responses?

hey folks ive been thinkin a lot about api performance lately esp with increasin user loads were seein some endpoints gettin hit pretty hard and im wonderin about the sweet spot for intro-in caching is it purely based on request volume or are there other factors like data volatility or complexity of the underlyin queries that should drive the decision whats your go-to strategy for decidin when and where to cache api responses