Here are some common and some less common greeting formulas in Spanish (there are so many!):
This one is probably the most common one. You can use it everywhere. It literally means “how are you?” (using estar, as in what’s your current status/condition).
This one is also very common. The literal translation would be something like “how so?” The full construction would be “¿qué tal estás?” but most times we just say the first part. You can also use this one everywhere.
Now here are some slang/regional/uncommon ones along with some comments:
This one is commonly used in many Latin American countries, and it literally means “what wave?” but “wave”, in general, means “flow” or “vive.” It’s somehow similar to the Irish term “craic”: good craic, bad craic, what’s the craic? Buena onda, mala onda, ¿qué onda?
Literally “what happened?” It can be used with its literal meaning (as in “I want to know what happened”) but, specifically in Mexico, it’s sometimes used as a greeting.
Same thing, but in the present tense. It’s pretty international. It’s like saying “what’s happening?” In Spain, it's often intonated as an exclamation: ¡Qué pasa!
¿Cómo lo llevas? / ¿Qué tal lo llevas?
This one is used mostly in Spain, and it means, more or less, “how are you dealing with it,” where “it” is just “it,” in general, as in “life” or “journey,” or “everything.”
¿Qué tal te va? / ¿Cómo te va?
It’s kind of like saying “how is everything going with you?" It can be used mostly everywhere.
¿Qué tal vas?
This one is used in northern Spain, specifically.
This one is very international, and it literally means “what is there?” in an existential quantifying way, as in “what exists [in your world]?"
Same thing, but in the past tense. Commonly used in Mexico. It’s sometimes slangishly written as “¿quihubo?”
¿Cómo te sientes?
Literally “how do you feel/how are you feeling.” It’s sometimes used in the Caribbean as a greeting, and we think it’s a very nice formula.
¿Cómo has estado?
Literally “how have you been?” It has a perfect aspect to it (as in “how have you been up to this very moment?”). It’s commonly used in Colombia, among other places.
In Spain, this expression is often used as in “what are you saying?” In Mexico, however, it’s often used as a greeting.
¿Qué hay de nuevo?
What’s new? This is what Bugs Bunny used to say in the Spanish translation.