During the summer we were staying in one of eight cottages so there were plenty of other guests around too. On many a morning a fellow guest would walk by our cottage with a genuine smile, saying, "Good morning. How are you?" Friendly. Pleasant. A nice greeting to start the day. However, it was a fly-by question. By the time they had got to the end of the sentence they would actually be long gone, completely out of view around the corner or attending to their recycling in the barn. I realised it's a question requiring no answer. It's a way of saying, "Hope all is okay but if it isn't I don't need to hear about it."
In the eyes of a Brit there isn't anything much worse than casually asking 'How are you?" as a greeting and someone actually launching in to a long diatribe about their achey knees, how their day got off to a terrible start thanks to an exploding coffee machine and how the rest of the day isn't looking too bright either. Telling a Brit about your woes is just not done, even if they enquire about your health.
When a Brit asks you how you are you say fine. Nothing more. It's a rhetorical question. Don't share how you actually are. We're not actually that interested. It's us being polite.
Unless.... unless we are actually, genuinely interested and we are having a conversation with you. For example, we do care about how life is going for our friends, family and those with any significant relationship in our lives. On the contrary, if we don't actually know you, then the question is merely politeness.
Still not clear? Try this. If you, for example, are checking in to a hotel and the person behind the reception desk asks "How are you today?" you do not relay every detail of your horrific car journey along the M25 and what it has done to your nerves. You do not share the epic state of the pounding in your head, how tired you are and how you really just want to have a lie down before dinner. You say, "I'm fine thank you. How are you?" As a response you can expect a "Very well, thank you." Then you can check in. The hotel worker doesn't know you. He doesn't need or want to know the ins and outs of your personal life. This applies to shop workers, customer service workers and officials. In short, if you don't know a person you answer "How are you?" with "Fine, thank you."