"Comment allez-vous ?" (formal)
You can also use:
* "Ça va ?" (informal, literally "How's it going?")
* "Comment vas-tu ?" (informal, for someone you know well)
Here are some common responses:
* "Bien, merci." (Good, thank you.)
* "Pas mal, merci." (Not bad, thank you.)
* "Très bien, merci." (Very well, thank you.)
* "Ça va." (It's going.)
* "Je vais bien." (I am well.)