In french, the words that come with the greeting are as important as the greeting itself. A same expression can therefore be used in different context, but preceeded or followed by different words:
Most formal version (hierarchical or commercial context):
-Bonjour, [titre], comment allez-vous ?
-Pour le mieux, merci. Et vous-même ?
-Très bien, je vous remercie.
"Normally polite" version:
-Bonjour, comment allez-vous ? (Without adding the title of the person we speak to)
-Très bien, merci, et vous ? ("Vous-même" vs "vous" makes the difference here)
-Ça va bien, merci ("Ca va bien" is not too formal but is still ok as an answer)
Less formal version (suitable for co-workers as an example, or well-established commercial relationships):
Bonjour ! Vous allez bien ? ("Vous allez" is less formal than "allez-vous")
Bonjour, comment ça va ? ("Ça va" is also less formal than "allez-vous")
Bonjour ! Ça va ? (Removing "comment" is even less formal but still OK)
Ça va bien, merci, et vous ? (Like in the "normally polite" section)
Très bien, merci, et vous? (Like in the "normally polite" section)
Ça va ça va, merci ! Et vous ? (Repeating "ça va" is less formal and more "friendly", but is still OK)
On fait aller, merci ! Et vous ? (Similarly, "on fait aller" is less formal and more "friendly", but is still OK)
Friendly version:
Salut, ça va ?
Salut, tu vas bien ?
Salut, comment tu vas ?
Hello ! Comment va ?
Salut ! Ça va bien ? (As a question, that's friendly. Way less formal than as an answer (see above))
Ça va ! Et toi ?
Pas mal, et toi ? (This is the exact equivalent of "Not too bad!" in english)
Oui, bien, et toi ?
On fait aller, et toi ?
Tranquillement, et toi ?
Colloquial/slang:
Salut ! ça roule ?
Salut ! La pêche ?
Salut ! La forme ?
Salut ! Ça gaze ?
Salut ! Ça boume ?
Etc... you can be creative. And this evolves every day. I actually don't know what they say in high-schools at the time being.
Any of the above (Ça roule !, la pêche, etc), or also:
Tranquilou ! Et toi ?
Pépère, et toi ?
Tranquille, et toi ?
Etc... you can be creative as well. And it evolves the same way as the questions.