Mieux vaut prévenir que guérir

Literal translation: Better preventing than curing
English translation: An ounce of prevention is worth a pound of cure

On n'est pas sortis de l'auberge

Literal translation: We are not out of the inn
English translation: We are not out of the woods

Mon petit doigt m'a dit

Literal translation: My little finger told me
English translation: A little bird told me

Tu me fais marcher

Literal translation: You make me walk
English translation: You pull my leg

Faire d'une pierre deux coups

Literal translation: To make from one stone two shots
English translation: To kill two birds with one stone

On n'apprend pas à un vieux singe à faire la grimace

Literal translation: One doesn't teach an old monkey to make a face
English translation: You can't teach an old dog new tricks

Il pleut des cordes

Literal translation: It rains ropes
English translation: It rains cats and dogs