You must know which side your bread is buttered on.

你必须知道自己的利益所在。

Justin: I just hope you know which side your bread is buttered on. Nowadays, good jobs are hard to come by.

贾斯汀：我只是希望你能清楚什么对自己最有利。现在，要找份好工作可不容易。

You should know which side of your (India's) bread is buttered.

你应该知道怎样才是对印度最有利的。