“Как дела?” and “как у тебя дела?” which one to use?

Question

In my book the meaning of как дела? is given as how are you?

Also the meaning of как у тебя дела? is given as how are you?

So which one should I use?

Answer 1

"Как дела?" can be roughly translated as "How are things?"

"Как у тебя дела?" -> "How are things with you?"

So one is just a shorter version of the other.

There is also the polite version: "Как у вас дела?". For more background on the тебя/вас distinction, see this question.

Answer 2

'как дела?' is more like a polite way to start a conversation, compare to:

how are you doing? fine, and you? i'm ok.

'как у тебя дела?' shows more interest in the actual state of things of a person you have a conversation with. The difference is subtle, yet I think it exists.