Here's what's funny, it's often a question but we don't necessarily want an answer. For example,  

"Hey, what's up?" We don't actually mean  tell me everything you got going on,  

the answer to that is "Not much." Another greeting, "Hey, how's it going?"  

Again, we're not asking you to really tell us how  things are going for you. The answer to that is  

"Good." Or you could say "Hey what's going  on?" Again, we don't need to know what you  

really have going on. It's just a greeting  and to that you could say "Not much." 

Now my dad, when he would go on runs around the  town and he would pass somebody else running,  

he would always say "How are you doing?" "How you doin'?" short for "How are you doing?" 

How are you doing? That's another good  greeting. Again the answer is just  

"Fine." If it's before noon,  my favorite greeting is  

"Morning!" I use this as I walk around the  neighborhood in the morning and see neighbors.