Different people are treated differently. Especially in Chinese.
Acquaintances or close friends or family are treated casually. That doesn't mean you don't care about them. It shows that you are close, you are intimate. So only in a horror movie will my dad say "ni hao" to me. I'm your son, dad. You don't remember me? In Chinese, when somebody says thank you — "谢谢", it's polite to say "不客气", which means "no need to be polite", which is paradoxical. But anyway, we don't say "hello" to friends in Chinese, because that's too "客气", too polite, like a stranger. You can simply say something like "hey" in Chinese to your friends and it's fine. With your parents you don't need any greetings, right. You can say "老师好" (teacher good) or "××老师好" (×× is the teacher's name) to your teacher. Or simply say his/her name as a greeting. Sometimes when you come across a friend in the street, you can ask "去哪呢" (where are you going). There used to be a time when people greet each other by asking "吃了吗" (have you had meal), which is silly and is not very common today.
If you have to be polite to or respectful to somebody, then of course you'll need to speak more formally. For example, you should use "您 nin" instead of "你 ni". In most cases you should call them with their first name followed by their position. So when you say hello to your boss whose name is Li, you should say "manager Li nin hao", "manager Li good morning". I think that's because in China people's status/position is somewhat more consciously considered. There is an interesting phenomenon that people never call you vice-something if you're in a secondary position. So if you're a vice-president, they will call you president.
Well, as you can see there're many rules or conventions in greetings, most of which are different across cultures. You can ask "how is your health" in some countries, but in China you only ask that to elders. There's no "how are you" in Chinese, only "you good".