As a general rule, I find "how are you" more a nicety / acknowledgment (similar to hello) than an inquiry as to how I am really doing. I generally answer "well/fine/meh. thanks."

I don't think people REALLY want to know to the depths of how I am, either. If things are going well, though, I don't think they truly want to know HOW well, either.

(*there is only 1 person in my life (she is 20 years old / half my age and wise since she was born) that asks me "how are you?" and means it. The first time it happened, I was actually surprised! )