Actually, we don't have a commonly-used phrase for "How are you?". Some people like me say "밥 먹었어?". In this case, the conversation usually goes like this: A : 안녕? Hi? B : 어, 왔어? Yup, here you are. A : 밥 먹었어? How are you? If B didn't have breakfast/lunch/dinner, there will be some reason like B doesn't feel well, something upsets B so B couldn't eat anything at all. Or if B had breakfast/lunch/dinner, then A and B would talk about whatever they want. About "How are you?" ㅡ considering its literal meaning ㅡ I'd be embarrassed because its meaning is way too general and sorta heavy(in Korean, I mean). I'd wonder what they intend to know about by saying it, so I'll hesitate to how to answer or just analyze it for an hour or two... Who knows? After all I had to learn how to be casual about it while learning English. You could say 잘 있었어? or 어떻게 지내고 있니? or 잘 지냈어? as 엘리자베스 and Lucy suggests, but it's not that common and we don't say it to someone we see everyday. To make it honorific, just add the ending "요" at the end of each one.

we can say that 너는 어떻게 지내고 있니??( how are you??) or 오늘 하루는 어떠했니??(how are you today??)

LITERALLY YOU CAN SAY '어때?' ,'요즘 어때?' , as other guys answered, But COLLOQUIALLY THEY DON'T SAY LIKE '너는 어떻게 지내고 있니??' nor '오늘 하루는 어떠했니??' It can be WRITTEN on a letter though, I WANT TO LET U KNOW HOW TO SAY 'HOW ARE YOU' COLLOQUIALLY IN REAL, SITUATION #1 (a bit for fun though, but it's same in English speaking culture, IMO) When you just met a person and you want to talk to him, you can say 나 그쪽에게 관심있어요 (i have an interest in you) SITUATION #2 Just usually say that to your friend or colleague or whoever around you you can say '(요즘 or 요새) 잘 지내?' '잘 있어?'(usually when you are talking to a person on phone)(r u doing well?) or '(하는) 일은 잘 돼가?' (can be colloquially translated as 'What's going on? or How's it going?, but literally 'Is what you 've been doing going well ?' SITUATION #3 JUST HABITUALLY SAY THAT TO PEOPLE AROUND YOU you can say '안녕', as 'how are you?' just means a bit more answerable than 'hello' or 'hi Hope you learn the 'REAL' language

One I was taught that I use all the time is 잘있었요? Its like have you been good? You can also just say it back in response to say Im good, Im ok. Just change the intonation of your voice at the end, rising for a question, falling for a statement. I think its maybe quite a casual way of asking, you'd have to get a native to explain the difference between using 잘있었요? and 너는 어떻게 지내고 있니? as I didn't actually know the two ways Mr Harry told you, so Cheers Mr Harry lol I learnt a new phrase too!

Harry's comment is correct, well.. more short sentence is just "안녕~~" hh that is hello~~