How's it going?

How's everything?

How's life?

(This means "How are you?" not "Where are you going?")

What's up?

What's happening?

(What are you doing now?)

What's new?

Guess what?

(What interesting has happened since I last saw you?)

(I want to tell you something. Ask me about it.)
(The appropriate response to this is "What?")

A: Guess what?

A: I just got a new job.

B: What?

B: Congratulations!