Formal:
* Здравствуйте, как дела? (Zdravstvuyte, kak dela?) - This is the most formal way to ask, suitable for addressing someone you don't know well or someone older than you.
* Здравствуйте, как у Вас дела? (Zdravstvuyte, kak u Vas dela?) - This is another formal option, similar to the previous one but using the polite "u Vas" instead of "kak dela."
Informal:
* Привет, как дела? (Privet, kak dela?) - This is the most common and casual way to ask, suitable for friends and family.
* Привет, как ты? (Privet, kak ty?) - This is another informal option, similar to the previous one but using the familiar "ty" instead of "dela."
More specific:
* Как дела? (Kak dela?) - This is a very informal and casual way to ask, but it's only used if you already know the person well.
* Как жизнь? (Kak zhizn?) - This is a slightly more informal way to ask than "kak dela" and means "How is life?"
The best choice will depend on the specific situation.