Some short greetings are: (informal) "Na du", "Hey du", "Hallöchen" "Was geht ab? "

Ohoh, careful with "How are you". There's something you maybe don't know if you speak English. In German, this question is reserved for people you already know. You might start asking this question maybe the third time you meet someone, in case you like them - it's a personal question, after all. Just so that you know. So, in addition to the others: It's common to go for "Good morning/evening". "Guten Morgen" - also short and more informal just "Morgen", "Guten Abend" - short and more informal also "n'Abend". Those are okay in informal settings, too. Even if you say them completely. But "Good day" / "Guten Tag" is stiff and formal. So, there is a gap in this trick during certain hours :) ("Tag, <Name>") is okay as a greeting in informal settings, but in my personal feeling, this lacks affection. I would not say that to my family or close friends.) There are also regional greetings which can be nice, too. But I'll keep them out of here. "Hey" and "hi" are okay too. And "Hallo, <Name>" is of course also there.

some greetings I know are:"Wie geht's? (informal),"Wie geht es Ihnen?"(formal ). That means How are you?