The question "How are you?" as a greeting was created only to get the conversational ball rolling - verbal oil, if you will, on possibly troubled waters. It need not be answered truthfully. There are ways and ways to respond.
The most Perfectly Proper response is, of course, "Very well, thank you. And you?" whether or not you are, in fact, very well. Etiquetteer's beloved Ellen Maury Slayden so decreed to her nieces, who she admonished for answering "Fine."* One could also deflect to the weather ("Beautiful day!") or the greeter ("Better for seeing you, my dear"). For those who are scrupulously honest but in a bad mood, Etiquetteer remembers from years ago a woman who would simply answer "Thank you," acknowledging the consideration of being asked, but not divulging her True Inner State. But this can seem rather brusque, and even call attention to one's reserve.
What ought to be avoided are an accounting of Negative Physical Symptoms. No one needs an Organ Recital of one's various ailments and pains - unless one is being greeted in a hospital bed. Etiquetteer also recommends avoiding comments on the political scene, especially in an election year. Etiquetteer will never forget greeting a Somewhat Eccentric Elderly Lady with a "How are you this evening?" and getting a somewhat hazy doom-and-gloom scenario on the Political Crisis of the Moment.
Please, ladies and gentlemen, spare us all and give us a nice "Very well, thank you!"
And please spare us all a speech. Any response to "How are you?" shouldn't take more than six words.
*"Fine," of course, is yet another example of Improper Slang that grew with frequent use to become Perfectly Proper." Etiquetteer has been known to shoot a look at That Mr. Dimmick Who Thinks He Knows So Much, who will often answer with "Fine as frog's hair," aping Richard Cromwell in Jezebel (1938).