Harvard University professor Stephen Pinker believes grammatical rules should be rejected under certain circumstances, such as if they're arbitrary, if great writers have "routinely flouted" them, and if fixing a sentence to be grammatically correct makes it "clumsier and less clear."
Those rules, however, can be helpful in situations where you need to be formal.
His advice for how to use the right words and phrases at the right time?
"Look it up.
Consult a modern usage guide or a dictionary with usage notes."