French phrase
Il vaut mieux ~.
Meaning
It's better to ___.
When to use it
It advises the best course of action for now. It is gentle advice, not a strong command.
Example dialogue
Il vaut mieux réserver les billets à l'avance.
It's better to book the tickets in advance.
Bonne idée, je vais le faire tout de suite.
Good idea, I'll do it right away.