When someone asks how you are, and you want to ask how they are in return, there are many ways you can respond. Below are some common phrases you can use.
"How/What about yourself?"
"How are you doing?"
"And yourself?" or just "Yourself?"
"And how have you been?"
"How's it going with you?"
"How are things on your end?"
"How's everything with you?"
"Have you been doing ok?"
I hope this helps.
For more articles on conversations, questions and responses, and common phrases, please visit our archive!
Asking how someone is: http://www.learnersdictionary.com/qa/are-you-sick-or-how-are-you-feeling
Agreeing with someone: http://www.learnersdictionary.com/qa/you-too-and-same-here
Sending formal e-mails: http://www.learnersdictionary.com/qa/greetings-for-formal-emails