You can answer in the way you like to do.

Sometimes, I respond:

 - All good, thanks. And you? / what about you?
 - Fine, and you?
 - Fine, thanks.

In your case, since you usually say "hi" or "hello", you can add:

 - Oh, hi, how are you?
 - Hello there _I think I read this response from a PSX videogame calle Yu-Gi-Oh! Forbidden Memories_ :)