It's possible to say: Not too bad. Not doing too bad. I'm not doing too bad. Not bad, could be worse. Pretty good. Wonderful! Fine. I'm all right. Can't complain. Couldn't be better! Never better! Actually "How are you?" is more like a greeting, not really a question! So when you want to say Hello to someone, you could use "How are you (today)?" instead :D

The possible answers: 1) Fine. - Straight and simple answer. 2) Not bad. - More friendly-sounding answer than "fine". 3) I am fine, thank you. - A formal answer. 4) Very well, thank you. - A people who prefers to be grammatically proper might answer this way. The question "How...?" should be answered with an adverb. 5) Good / Pretty good. - A more casual answer. Hope it will help you. 英語の勉強は頑張ってください。^_^

I'm fine, thanks! Fine! I'm not so well.

Most people who ask are not really interested in the answer, they just ask to be polite, so any answer of the above is fine, except I would try to use the positive ones just not to put a negative tone on the whole conversation. For example I am well/fine, thank you, and you? Remember, the asker is not usually interested in knowing the details of your sorrows, and if you tell them they may actually not appreciate it. (Chances are that if you are walking and talking you are well enough to say "I am well") If you are really not well, and the person who is asking is someone you know fairly well, and you feel the person is actually sincerely wanting to know about your welfare, which sometimes does happen, and you don't feel like sharing your personal business of how you are feeling and why, what you can do is to answer not about your feelings, but rather about your surroundings/events. You can say for example, Oh, today I had a good day at school/university/work. Oh, I am all taken up by an interesting book I have been reading. I am enjoying the beautiful sunshine. I just went for a walk and I feel refreshed. I am really excited that a new school term is starting soon. Well, today I happy that I have ran into a friend I had not seen in a while. etc etc. Such answers remove the focus of the asker from your deeper feelings/personal business, and give opportunity to turn the conversation to something you enjoy talking about.

Honestly "How are you" IS normally a stupid question. Oftentimes, people really don't care but they'll ask anyways. How you answer is not a problem but if you want to spice it up, here's some answers: Positives I am great! Great! Today is wonderful! I am good. I'm good. I'm good. It's such a beautiful day today. I'm feeling great! The weather is so nice outside. Neutrals: I'm hanging in there (my dad often says this) My dad also often says: "I'm still kickin'" (meaning he's still alive) Glad to be inside. It is hot outside! Glad to be inside. It's so windy out there. Glad to be inside. It's so cold. Negatives I've been better (often said when one's stressed out, like too much work at their job) Eh, chilled to the bone. It's snowing outside. Also remember that it is generally polite to ask the asker how they are, so you'll want to include that in your responses.