Formal:
* आप कैसे हैं? (aap kaise hain?) - This is the most common and formal way to ask "how are you?" It's used when addressing someone older than you or someone you don't know well.
Informal:
* कैसे हो? (kaise ho?) - This is the informal way to ask "how are you?" and is used with friends and family.
* तुम कैसे हो? (tum kaise ho?) - This is another informal way to ask "how are you?" and is used with friends and family, similar to "kaise ho?".
Other options:
* आप कैसे चल रहे हैं? (aap kaise chal rahe hain?) - This means "how are you doing?" and is a more polite and formal way to ask.
* आप कैसे हैं? (aap kaise hain?) - This means "how are you?" and is a more common and informal way to ask.
Note:
* The word "aap" is used when addressing someone formally, while "tum" is used informally.
* You can also add "ji" at the end of the sentence for extra politeness, like "aap kaise hain ji?" or "kaise ho ji?".
Remember: The best way to choose which phrase to use depends on the situation and your relationship with the person you are talking to.