Formal:
* Bonjour, comment allez-vous ? (This is the most formal way to say "Hello, how are you?")
Informal:
* Salut, ça va ? (This is a more casual way to say "Hi, how are you?")
* Coucou, ça va ? (This is even more informal and used with friends or family)
More casual and playful:
* Salut, comment tu vas ? (This is used with friends, family, or people you know well)
* Coucou, comment tu vas ? (Even more casual than the previous one)
You can also use "Bonjour" or "Salut" without the "how are you" part, which would be a simple greeting.
The best choice depends on the context and who you are talking to.