It depends a lot on the country and the culture.
In some countries/cultures questions like "How are you" don't expect a real response, they will get generic responses.
How are you?
Good and you?
They will say this no matter if they are good or bad. In other cultures the response may be different. Sometimes people don't like to say that things are good so they will say okay or some such.
In some countries they however it is actually only normal to ask close friends how they are. There asking how are you is an opening to discuss their life problems.
If you are looking for some generic responses then here are some.
How are you
could complain but not much point.(Said with a smile)
If someone asks "how are things going". You can use the responses from above or some also try to play on the question by saying things like
well they are going, i guess.
In some cultures people are reluctant to say that things are going good. So they will predominantly say that things are going okay, or some such. 1 reason is a wish to not tempt fate. i.e. if you say things are good it's like asking the universe to make your life worse.
So an example of a longer form response I may use myself is
How are you
Well ok I guess, Things could be better but then again they could also be much worse, so I shouldn't/can't complain. How about yourself?