Formal:
* How are you? (This is the most common and literal translation)
* How are things going?
Informal:
* What's up?
* How's it going?
* What's new?
Other uses:
* "Que tal" can also be used as a greeting, similar to "hello."
* It can also be used to express interest in something, similar to "how about..." (e.g., "Que tal una cerveza?" - "How about a beer?")
The best translation will depend on the context of the conversation and your level of formality.