How are you?  This is a standard question yet your answer doesn't have to be standard.  

Common answers: I'm: fine, good, o.k..  I could be better or not bad

More fun ways to answer this questions are:  I'm over the moon./I'm in 7th heaven./ I 'm on cloud 9./ I'm tickled pink. = all mean that you are very happy

or I feel blue. = sad

    I am a bit under the weather. = so/so or a bit sick

    I could be better.