They had me at Hello

Is anyone else eluded by greetings? I always find it hard to choose the proper way to greet someone, especially since there are so many ways to do so. Often, as well, I wonder if people hear or my greeting when passing in the hall. And speaking of that, if two people are walking towards each other down opposite sides of a hallway, what is the proper distance away at which they should be greeted. Because if you see each other, then you have to wait until your close enough to greet someone. If you greet them when they are too far away, then you still have all that space to cover and you feel like you should say more, but its hard to have a long distance conversation like that. But when they're close, there is also awkwardness because you don't know their thoughts about how you are greeting them, but then its all ok once you have passed each other.